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While the GCC and Clang compilers already define __ASSEMBLER__
automatically when compiling assembly code, __ASSEMBLY__ is a
macro that only gets defined by the Makefiles in the kernel.
This can be very confusing when switching between userspace
and kernelspace coding, or when dealing with UAPI headers that
rather should use __ASSEMBLER__ instead. So let's standardize on
the __ASSEMBLER__ macro that is provided by the compilers now.
This is mostly a mechanical patch (done with a simple "sed -i"
statement), with some manual tweaks in <asm/frame.h>, <asm/hw_irq.h>
and <asm/setup.h> that mentioned this macro in comments with some
missing underscores.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250314071013.1575167-38-thuth@redhat.com
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common_interrupt() and related variants call kvm_set_cpu_l1tf_flush_l1d(),
which is neither marked noinstr nor __always_inline.
So compiler puts it out of line and adds instrumentation to it. Since the
call is inside of instrumentation_begin/end(), objtool does not warn about
it.
The manifestation is that KCOV produces spurious coverage in
kvm_set_cpu_l1tf_flush_l1d() in random places because the call happens when
preempt count is not yet updated to say that the kernel is in an interrupt.
Mark kvm_set_cpu_l1tf_flush_l1d() as __always_inline and move it out of the
instrumentation_begin/end() section. It only calls __this_cpu_write()
which is already safe to call in noinstr contexts.
Fixes: 6368558c3710 ("x86/entry: Provide IDTENTRY_SYSVEC")
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/3f9a1de9e415fcb53d07dc9e19fa8481bb021b1b.1718092070.git.dvyukov@google.com
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All MSI vectors are multiplexed into a single notification vector when
posted MSI is enabled. It is the responsibility of the notification vector
handler to demultiplex MSI vectors. In the handler the MSI vector handlers
are dispatched without IDT delivery for each pending MSI interrupt.
For example, the interrupt flow will change as follows:
(3 MSIs of different vectors arrive in a a high frequency burst)
BEFORE:
interrupt(MSI)
irq_enter()
handler() /* EOI */
irq_exit()
process_softirq()
interrupt(MSI)
irq_enter()
handler() /* EOI */
irq_exit()
process_softirq()
interrupt(MSI)
irq_enter()
handler() /* EOI */
irq_exit()
process_softirq()
AFTER:
interrupt /* Posted MSI notification vector */
irq_enter()
atomic_xchg(PIR)
handler()
handler()
handler()
pi_clear_on()
apic_eoi()
irq_exit()
process_softirq()
Except for the leading MSI, CPU notifications are skipped/coalesced.
For MSIs which arrive at a low frequency, the demultiplexing loop does not
wait for more interrupts to coalesce. Therefore, there's no additional
latency other than the processing time.
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240423174114.526704-9-jacob.jun.pan@linux.intel.com
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Pull kvm updates from Paolo Bonzini:
"S390:
- Changes to FPU handling came in via the main s390 pull request
- Only deliver to the guest the SCLP events that userspace has
requested
- More virtual vs physical address fixes (only a cleanup since
virtual and physical address spaces are currently the same)
- Fix selftests undefined behavior
x86:
- Fix a restriction that the guest can't program a PMU event whose
encoding matches an architectural event that isn't included in the
guest CPUID. The enumeration of an architectural event only says
that if a CPU supports an architectural event, then the event can
be programmed *using the architectural encoding*. The enumeration
does NOT say anything about the encoding when the CPU doesn't
report support the event *in general*. It might support it, and it
might support it using the same encoding that made it into the
architectural PMU spec
- Fix a variety of bugs in KVM's emulation of RDPMC (more details on
individual commits) and add a selftest to verify KVM correctly
emulates RDMPC, counter availability, and a variety of other
PMC-related behaviors that depend on guest CPUID and therefore are
easier to validate with selftests than with custom guests (aka
kvm-unit-tests)
- Zero out PMU state on AMD if the virtual PMU is disabled, it does
not cause any bug but it wastes time in various cases where KVM
would check if a PMC event needs to be synthesized
- Optimize triggering of emulated events, with a nice ~10%
performance improvement in VM-Exit microbenchmarks when a vPMU is
exposed to the guest
- Tighten the check for "PMI in guest" to reduce false positives if
an NMI arrives in the host while KVM is handling an IRQ VM-Exit
- Fix a bug where KVM would report stale/bogus exit qualification
information when exiting to userspace with an internal error exit
code
- Add a VMX flag in /proc/cpuinfo to report 5-level EPT support
- Rework TDP MMU root unload, free, and alloc to run with mmu_lock
held for read, e.g. to avoid serializing vCPUs when userspace
deletes a memslot
- Tear down TDP MMU page tables at 4KiB granularity (used to be
1GiB). KVM doesn't support yielding in the middle of processing a
zap, and 1GiB granularity resulted in multi-millisecond lags that
are quite impolite for CONFIG_PREEMPT kernels
- Allocate write-tracking metadata on-demand to avoid the memory
overhead when a kernel is built with i915 virtualization support
but the workloads use neither shadow paging nor i915 virtualization
- Explicitly initialize a variety of on-stack variables in the
emulator that triggered KMSAN false positives
- Fix the debugregs ABI for 32-bit KVM
- Rework the "force immediate exit" code so that vendor code
ultimately decides how and when to force the exit, which allowed
some optimization for both Intel and AMD
- Fix a long-standing bug where kvm_has_noapic_vcpu could be left
elevated if vCPU creation ultimately failed, causing extra
unnecessary work
- Cleanup the logic for checking if the currently loaded vCPU is
in-kernel
- Harden against underflowing the active mmu_notifier invalidation
count, so that "bad" invalidations (usually due to bugs elsehwere
in the kernel) are detected earlier and are less likely to hang the
kernel
x86 Xen emulation:
- Overlay pages can now be cached based on host virtual address,
instead of guest physical addresses. This removes the need to
reconfigure and invalidate the cache if the guest changes the gpa
but the underlying host virtual address remains the same
- When possible, use a single host TSC value when computing the
deadline for Xen timers in order to improve the accuracy of the
timer emulation
- Inject pending upcall events when the vCPU software-enables its
APIC to fix a bug where an upcall can be lost (and to follow Xen's
behavior)
- Fall back to the slow path instead of warning if "fast" IRQ
delivery of Xen events fails, e.g. if the guest has aliased xAPIC
IDs
RISC-V:
- Support exception and interrupt handling in selftests
- New self test for RISC-V architectural timer (Sstc extension)
- New extension support (Ztso, Zacas)
- Support userspace emulation of random number seed CSRs
ARM:
- Infrastructure for building KVM's trap configuration based on the
architectural features (or lack thereof) advertised in the VM's ID
registers
- Support for mapping vfio-pci BARs as Normal-NC (vaguely similar to
x86's WC) at stage-2, improving the performance of interacting with
assigned devices that can tolerate it
- Conversion of KVM's representation of LPIs to an xarray, utilized
to address serialization some of the serialization on the LPI
injection path
- Support for _architectural_ VHE-only systems, advertised through
the absence of FEAT_E2H0 in the CPU's ID register
- Miscellaneous cleanups, fixes, and spelling corrections to KVM and
selftests
LoongArch:
- Set reserved bits as zero in CPUCFG
- Start SW timer only when vcpu is blocking
- Do not restart SW timer when it is expired
- Remove unnecessary CSR register saving during enter guest
- Misc cleanups and fixes as usual
Generic:
- Clean up Kconfig by removing CONFIG_HAVE_KVM, which was basically
always true on all architectures except MIPS (where Kconfig
determines the available depending on CPU capabilities). It is
replaced either by an architecture-dependent symbol for MIPS, and
IS_ENABLED(CONFIG_KVM) everywhere else
- Factor common "select" statements in common code instead of
requiring each architecture to specify it
- Remove thoroughly obsolete APIs from the uapi headers
- Move architecture-dependent stuff to uapi/asm/kvm.h
- Always flush the async page fault workqueue when a work item is
being removed, especially during vCPU destruction, to ensure that
there are no workers running in KVM code when all references to
KVM-the-module are gone, i.e. to prevent a very unlikely
use-after-free if kvm.ko is unloaded
- Grab a reference to the VM's mm_struct in the async #PF worker
itself instead of gifting the worker a reference, so that there's
no need to remember to *conditionally* clean up after the worker
Selftests:
- Reduce boilerplate especially when utilize selftest TAP
infrastructure
- Add basic smoke tests for SEV and SEV-ES, along with a pile of
library support for handling private/encrypted/protected memory
- Fix benign bugs where tests neglect to close() guest_memfd files"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (246 commits)
selftests: kvm: remove meaningless assignments in Makefiles
KVM: riscv: selftests: Add Zacas extension to get-reg-list test
RISC-V: KVM: Allow Zacas extension for Guest/VM
KVM: riscv: selftests: Add Ztso extension to get-reg-list test
RISC-V: KVM: Allow Ztso extension for Guest/VM
RISC-V: KVM: Forward SEED CSR access to user space
KVM: riscv: selftests: Add sstc timer test
KVM: riscv: selftests: Change vcpu_has_ext to a common function
KVM: riscv: selftests: Add guest helper to get vcpu id
KVM: riscv: selftests: Add exception handling support
LoongArch: KVM: Remove unnecessary CSR register saving during enter guest
LoongArch: KVM: Do not restart SW timer when it is expired
LoongArch: KVM: Start SW timer only when vcpu is blocking
LoongArch: KVM: Set reserved bits as zero in CPUCFG
KVM: selftests: Explicitly close guest_memfd files in some gmem tests
KVM: x86/xen: fix recursive deadlock in timer injection
KVM: pfncache: simplify locking and make more self-contained
KVM: x86/xen: remove WARN_ON_ONCE() with false positives in evtchn delivery
KVM: x86/xen: inject vCPU upcall vector when local APIC is enabled
KVM: x86/xen: improve accuracy of Xen timers
...
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It is more accurate to check if KVM is enabled, instead of having the
architecture say so. Architectures always "have" KVM, so for example
checking CONFIG_HAVE_KVM in x86 code is pointless, but if KVM is disabled
in a specific build, there is no need for support code.
Alternatively, many of the #ifdefs could simply be deleted. However,
this would add completely dead code. For example, when KVM is disabled,
there should not be any posted interrupts, i.e. NOT wiring up the "dummy"
handlers and treating IRQs on those vectors as spurious is the right
thing to do.
Cc: x86@kernel.org
Cc: kbingham@kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Add sysvec_install() to install a system interrupt handler into the IDT
or the FRED system interrupt handler table.
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-28-xin3.li@intel.com
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FRED and IDT can share most of the definitions and declarations so
that in the majority of cases the actual handler implementation is the
same.
The differences are the exceptions where FRED stores exception related
information on the stack and the sysvec implementations as FRED can
handle irqentry/exit() in the dispatcher instead of having it in each
handler.
Also add stub defines for vectors which are not used due to Kconfig
decisions to spare the ifdeffery in the actual FRED dispatch code.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-23-xin3.li@intel.com
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idtentry_sysvec is really just DECLARE_IDTENTRY defined in
<asm/idtentry.h>, no need to define it separately.
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-3-xin3.li@intel.com
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There is no real reason to have a separate ASM entry point implementation
for the legacy INT 0x80 syscall emulation on 64-bit.
IDTENTRY provides all the functionality needed with the only difference
that it does not:
- save the syscall number (AX) into pt_regs::orig_ax
- set pt_regs::ax to -ENOSYS
Both can be done safely in the C code of an IDTENTRY before invoking any of
the syscall related functions which depend on this convention.
Aside of ASM code reduction this prepares for detecting and handling a
local APIC injected vector 0x80.
[ kirill.shutemov: More verbose comments ]
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@vger.kernel.org> # v6.0+
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 shadow stack support from Dave Hansen:
"This is the long awaited x86 shadow stack support, part of Intel's
Control-flow Enforcement Technology (CET).
CET consists of two related security features: shadow stacks and
indirect branch tracking. This series implements just the shadow stack
part of this feature, and just for userspace.
The main use case for shadow stack is providing protection against
return oriented programming attacks. It works by maintaining a
secondary (shadow) stack using a special memory type that has
protections against modification. When executing a CALL instruction,
the processor pushes the return address to both the normal stack and
to the special permission shadow stack. Upon RET, the processor pops
the shadow stack copy and compares it to the normal stack copy.
For more information, refer to the links below for the earlier
versions of this patch set"
Link: https://lore.kernel.org/lkml/20220130211838.8382-1-rick.p.edgecombe@intel.com/
Link: https://lore.kernel.org/lkml/20230613001108.3040476-1-rick.p.edgecombe@intel.com/
* tag 'x86_shstk_for_6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (47 commits)
x86/shstk: Change order of __user in type
x86/ibt: Convert IBT selftest to asm
x86/shstk: Don't retry vm_munmap() on -EINTR
x86/kbuild: Fix Documentation/ reference
x86/shstk: Move arch detail comment out of core mm
x86/shstk: Add ARCH_SHSTK_STATUS
x86/shstk: Add ARCH_SHSTK_UNLOCK
x86: Add PTRACE interface for shadow stack
selftests/x86: Add shadow stack test
x86/cpufeatures: Enable CET CR4 bit for shadow stack
x86/shstk: Wire in shadow stack interface
x86: Expose thread features in /proc/$PID/status
x86/shstk: Support WRSS for userspace
x86/shstk: Introduce map_shadow_stack syscall
x86/shstk: Check that signal frame is shadow stack mem
x86/shstk: Check that SSP is aligned on sigreturn
x86/shstk: Handle signals for shadow stack
x86/shstk: Introduce routines modifying shstk
x86/shstk: Handle thread shadow stack
x86/shstk: Add user-mode shadow stack support
...
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The left overs of a moved interrupt are cleaned up once the interrupt is
raised on the new target CPU. Keeping the vector valid on the original
target CPU guarantees that there can't be an interrupt lost if the affinity
change races with an concurrent interrupt from the device.
This cleanup utilizes the lowest priority interrupt vector for this
cleanup, which makes sure that in the unlikely case when the to be cleaned
up interrupt is pending in the local APICs IRR the cleanup vector does not
live lock.
But there is no real reason to use an interrupt vector for cleaning up the
leftovers of a moved interrupt. It's not a high performance operation. The
only requirement is that it happens on the original target CPU.
Convert it to use a timer instead and adjust the code accordingly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230621171248.6805-3-xin3.li@intel.com
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A control-protection fault is triggered when a control-flow transfer
attempt violates Shadow Stack or Indirect Branch Tracking constraints.
For example, the return address for a RET instruction differs from the copy
on the shadow stack.
There already exists a control-protection fault handler for handling kernel
IBT faults. Refactor this fault handler into separate user and kernel
handlers, like the page fault handler. Add a control-protection handler
for usermode. To avoid ifdeffery, put them both in a new file cet.c, which
is compiled in the case of either of the two CET features supported in the
kernel: kernel IBT or user mode shadow stack. Move some static inline
functions from traps.c into a header so they can be used in cet.c.
Opportunistically fix a comment in the kernel IBT part of the fault
handler that is on the end of the line instead of preceding it.
Keep the same behavior for the kernel side of the fault handler, except for
converting a BUG to a WARN in the case of a #CP happening when the feature
is missing. This unifies the behavior with the new shadow stack code, and
also prevents the kernel from crashing under this situation which is
potentially recoverable.
The control-protection fault handler works in a similar way as the general
protection fault handler. It provides the si_code SEGV_CPERR to the signal
handler.
Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-28-rick.p.edgecombe%40intel.com
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Use a dedicated entry for invoking the NMI handler from KVM VMX's VM-Exit
path for 32-bit even though using a dedicated entry for 32-bit isn't
strictly necessary. Exposing a single symbol will allow KVM to reference
the entry point in assembly code without having to resort to more #ifdefs
(or #defines). identry.h is intended to be included from asm files only
once, and so simply including idtentry.h in KVM assembly isn't an option.
Bypassing the ESP fixup and CR3 switching in the standard NMI entry code
is safe as KVM always handles NMIs that occur in the guest on a kernel
stack, with a kernel CR3.
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221213060912.654668-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Virtualization Exceptions (#VE) are delivered to TDX guests due to
specific guest actions which may happen in either user space or the
kernel:
* Specific instructions (WBINVD, for example)
* Specific MSR accesses
* Specific CPUID leaf accesses
* Access to specific guest physical addresses
Syscall entry code has a critical window where the kernel stack is not
yet set up. Any exception in this window leads to hard to debug issues
and can be exploited for privilege escalation. Exceptions in the NMI
entry code also cause issues. Returning from the exception handler with
IRET will re-enable NMIs and nested NMI will corrupt the NMI stack.
For these reasons, the kernel avoids #VEs during the syscall gap and
the NMI entry code. Entry code paths do not access TD-shared memory,
MMIO regions, use #VE triggering MSRs, instructions, or CPUID leaves
that might generate #VE. VMM can remove memory from TD at any point,
but access to unaccepted (or missing) private memory leads to VM
termination, not to #VE.
Similarly to page faults and breakpoints, #VEs are allowed in NMI
handlers once the kernel is ready to deal with nested NMIs.
During #VE delivery, all interrupts, including NMIs, are blocked until
TDGETVEINFO is called. It prevents #VE nesting until the kernel reads
the VE info.
TDGETVEINFO retrieves the #VE info from the TDX module, which also
clears the "#VE valid" flag. This must be done before anything else as
any #VE that occurs while the valid flag is set escalates to #DF by TDX
module. It will result in an oops.
Virtual NMIs are inhibited if the #VE valid flag is set. NMI will not be
delivered until TDGETVEINFO is called.
For now, convert unhandled #VE's (everything, until later in this
series) so that they appear just like a #GP by calling the
ve_raise_fault() directly. The ve_raise_fault() function is similar
to #GP handler and is responsible for sending SIGSEGV to userspace
and CPU die and notifying debuggers and other die chain users.
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20220405232939.73860-8-kirill.shutemov@linux.intel.com
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The bits required to make the hardware go.. Of note is that, provided
the syscall entry points are covered with ENDBR, #CP doesn't need to
be an IST because we'll never hit the syscall gap.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.582331711@infradead.org
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Kernel entry points should be having ENDBR on for IBT configs.
The SYSCALL entry points are found through taking their respective
address in order to program them in the MSRs, while the exception
entry points are found through UNWIND_HINT_IRET_REGS.
The rule is that any UNWIND_HINT_IRET_REGS at sym+0 should have an
ENDBR, see the later objtool ibt validation patch.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.933157479@infradead.org
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 interrupt related updates from Thomas Gleixner:
- Consolidate the VECTOR defines and the usage sites.
- Cleanup GDT/IDT related code and replace open coded ASM with proper
native helper functions.
* tag 'x86-irq-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/kexec: Set_[gi]dt() -> native_[gi]dt_invalidate() in machine_kexec_*.c
x86: Add native_[ig]dt_invalidate()
x86/idt: Remove address argument from idt_invalidate()
x86/irq: Add and use NR_EXTERNAL_VECTORS and NR_SYSTEM_VECTORS
x86/irq: Remove unused vectors defines
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Split up the #VC handler code into a from-user and a from-kernel part.
This allows clean and correct state tracking, as the #VC handler needs
to enter NMI-state when raised from kernel mode and plain IRQ state when
raised from user-mode.
Fixes: 62441a1fb532 ("x86/sev-es: Correctly track IRQ states in runtime #VC handler")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210618115409.22735-3-joro@8bytes.org
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Add defines for the number of external vectors and number of system
vectors instead of requiring the use of (FIRST_SYSTEM_VECTOR -
FIRST_EXTERNAL_VECTOR) and (NR_VECTORS - FIRST_SYSTEM_VECTOR)
respectively. Clean up the usage sites.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20210519212154.511983-3-hpa@zytor.com
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In VMX, the host NMI handler needs to be invoked after NMI VM-Exit.
Before commit 1a5488ef0dcf6 ("KVM: VMX: Invoke NMI handler via indirect
call instead of INTn"), this was done by INTn ("int $2"). But INTn
microcode is relatively expensive, so the commit reworked NMI VM-Exit
handling to invoke the kernel handler by function call.
But this missed a detail. The NMI entry point for direct invocation is
fetched from the IDT table and called on the kernel stack. But on 64-bit
the NMI entry installed in the IDT expects to be invoked on the IST stack.
It relies on the "NMI executing" variable on the IST stack to work
correctly, which is at a fixed position in the IST stack. When the entry
point is unexpectedly called on the kernel stack, the RSP-addressed "NMI
executing" variable is obviously also on the kernel stack and is
"uninitialized" and can cause the NMI entry code to run in the wrong way.
Provide a non-ist entry point for VMX which shares the C-function with
the regular NMI entry and invoke the new asm entry point instead.
On 32-bit this just maps to the regular NMI entry point as 32-bit has no
ISTs and is not affected.
[ tglx: Made it independent for backporting, massaged changelog ]
Fixes: 1a5488ef0dcf6 ("KVM: VMX: Invoke NMI handler via indirect call instead of INTn")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Lai Jiangshan <laijs@linux.alibaba.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87r1imi8i1.ffs@nanos.tec.linutronix.de
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Fix ~144 single-word typos in arch/x86/ code comments.
Doing this in a single commit should reduce the churn.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-kernel@vger.kernel.org
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Merge in the recent paravirt changes to resolve conflicts caused
by objtool annotations.
Conflicts:
arch/x86/xen/xen-asm.S
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Convert device interrupts to inline stack switching by replacing the
existing macro implementation with the new inline version. Tweak the
function signature of the actual handler function to have the vector
argument as u32. That allows the inline macro to avoid extra intermediates
and lets the compiler be smarter about the whole thing.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210210002512.769728139@linutronix.de
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To inline the stack switching and to prepare for enabling
CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK provide a macro template for system
vectors and device interrupts and convert the system vectors over to it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210210002512.676197354@linutronix.de
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Xen PV guests don't use IST. For double fault interrupts, switch to
the same model as NMI.
Correct a typo in a comment while copying it.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210120135555.32594-4-jgross@suse.com
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Xen PV guests don't use IST. For machine check interrupts, switch to the
same model as debug interrupts.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210120135555.32594-3-jgross@suse.com
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git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip
Pull xen fixes from Juergen Gross:
- A fix for a regression introduced in 5.11 resulting in Xen dom0
having problems to correctly initialize Xenstore.
- A fix for avoiding WARN splats when booting as Xen dom0 with
CONFIG_AMD_MEM_ENCRYPT enabled due to a missing trap handler for the
#VC exception (even if the handler should never be called).
- A fix for the Xen bklfront driver adapting to the correct but
unexpected behavior of new qemu.
* tag 'for-linus-5.11-rc6-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
x86/xen: avoid warning in Xen pv guest with CONFIG_AMD_MEM_ENCRYPT enabled
xen: Fix XenStore initialisation for XS_LOCAL
xen-blkfront: allow discard-* nodes to be optional
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When booting a kernel which has been built with CONFIG_AMD_MEM_ENCRYPT
enabled as a Xen pv guest a warning is issued for each processor:
[ 5.964347] ------------[ cut here ]------------
[ 5.968314] WARNING: CPU: 0 PID: 1 at /home/gross/linux/head/arch/x86/xen/enlighten_pv.c:660 get_trap_addr+0x59/0x90
[ 5.972321] Modules linked in:
[ 5.976313] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 5.11.0-rc5-default #75
[ 5.980313] Hardware name: Dell Inc. OptiPlex 9020/0PC5F7, BIOS A05 12/05/2013
[ 5.984313] RIP: e030:get_trap_addr+0x59/0x90
[ 5.988313] Code: 42 10 83 f0 01 85 f6 74 04 84 c0 75 1d b8 01 00 00 00 c3 48 3d 00 80 83 82 72 08 48 3d 20 81 83 82 72 0c b8 01 00 00 00 eb db <0f> 0b 31 c0 c3 48 2d 00 80 83 82 48 ba 72 1c c7 71 1c c7 71 1c 48
[ 5.992313] RSP: e02b:ffffc90040033d38 EFLAGS: 00010202
[ 5.996313] RAX: 0000000000000001 RBX: ffffffff82a141d0 RCX: ffffffff8222ec38
[ 6.000312] RDX: ffffffff8222ec38 RSI: 0000000000000005 RDI: ffffc90040033d40
[ 6.004313] RBP: ffff8881003984a0 R08: 0000000000000007 R09: ffff888100398000
[ 6.008312] R10: 0000000000000007 R11: ffffc90040246000 R12: ffff8884082182a8
[ 6.012313] R13: 0000000000000100 R14: 000000000000001d R15: ffff8881003982d0
[ 6.016316] FS: 0000000000000000(0000) GS:ffff888408200000(0000) knlGS:0000000000000000
[ 6.020313] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6.024313] CR2: ffffc900020ef000 CR3: 000000000220a000 CR4: 0000000000050660
[ 6.028314] Call Trace:
[ 6.032313] cvt_gate_to_trap.part.7+0x3f/0x90
[ 6.036313] ? asm_exc_double_fault+0x30/0x30
[ 6.040313] xen_convert_trap_info+0x87/0xd0
[ 6.044313] xen_pv_cpu_up+0x17a/0x450
[ 6.048313] bringup_cpu+0x2b/0xc0
[ 6.052313] ? cpus_read_trylock+0x50/0x50
[ 6.056313] cpuhp_invoke_callback+0x80/0x4c0
[ 6.060313] _cpu_up+0xa7/0x140
[ 6.064313] cpu_up+0x98/0xd0
[ 6.068313] bringup_nonboot_cpus+0x4f/0x60
[ 6.072313] smp_init+0x26/0x79
[ 6.076313] kernel_init_freeable+0x103/0x258
[ 6.080313] ? rest_init+0xd0/0xd0
[ 6.084313] kernel_init+0xa/0x110
[ 6.088313] ret_from_fork+0x1f/0x30
[ 6.092313] ---[ end trace be9ecf17dceeb4f3 ]---
Reason is that there is no Xen pv trap entry for X86_TRAP_VC.
Fix that by adding a generic trap handler for unknown traps and wire all
unknown bare metal handlers to this generic handler, which will just
crash the system in case such a trap will ever happen.
Fixes: 0786138c78e793 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc: <stable@vger.kernel.org> # v5.10
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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Lockdep state handling on NMI enter and exit is nothing specific to X86. It's
not any different on other architectures. Also the extra state type is not
necessary, irqentry_state_t can carry the necessary information as well.
Move it to common code and extend irqentry_state_t to carry lockdep state.
[ Ira: Make exit_rcu and lockdep a union as they are mutually exclusive
between the IRQ and NMI exceptions, and add kernel documentation for
struct irqentry_state_t ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201102205320.1458656-7-ira.weiny@intel.com
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 SEV-ES support from Borislav Petkov:
"SEV-ES enhances the current guest memory encryption support called SEV
by also encrypting the guest register state, making the registers
inaccessible to the hypervisor by en-/decrypting them on world
switches. Thus, it adds additional protection to Linux guests against
exfiltration, control flow and rollback attacks.
With SEV-ES, the guest is in full control of what registers the
hypervisor can access. This is provided by a guest-host exchange
mechanism based on a new exception vector called VMM Communication
Exception (#VC), a new instruction called VMGEXIT and a shared
Guest-Host Communication Block which is a decrypted page shared
between the guest and the hypervisor.
Intercepts to the hypervisor become #VC exceptions in an SEV-ES guest
so in order for that exception mechanism to work, the early x86 init
code needed to be made able to handle exceptions, which, in itself,
brings a bunch of very nice cleanups and improvements to the early
boot code like an early page fault handler, allowing for on-demand
building of the identity mapping. With that, !KASLR configurations do
not use the EFI page table anymore but switch to a kernel-controlled
one.
The main part of this series adds the support for that new exchange
mechanism. The goal has been to keep this as much as possibly separate
from the core x86 code by concentrating the machinery in two
SEV-ES-specific files:
arch/x86/kernel/sev-es-shared.c
arch/x86/kernel/sev-es.c
Other interaction with core x86 code has been kept at minimum and
behind static keys to minimize the performance impact on !SEV-ES
setups.
Work by Joerg Roedel and Thomas Lendacky and others"
* tag 'x86_seves_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (73 commits)
x86/sev-es: Use GHCB accessor for setting the MMIO scratch buffer
x86/sev-es: Check required CPU features for SEV-ES
x86/efi: Add GHCB mappings when SEV-ES is active
x86/sev-es: Handle NMI State
x86/sev-es: Support CPU offline/online
x86/head/64: Don't call verify_cpu() on starting APs
x86/smpboot: Load TSS and getcpu GDT entry before loading IDT
x86/realmode: Setup AP jump table
x86/realmode: Add SEV-ES specific trampoline entry point
x86/vmware: Add VMware-specific handling for VMMCALL under SEV-ES
x86/kvm: Add KVM-specific VMMCALL handling under SEV-ES
x86/paravirt: Allow hypervisor-specific VMMCALL handling under SEV-ES
x86/sev-es: Handle #DB Events
x86/sev-es: Handle #AC Events
x86/sev-es: Handle VMMCALL Events
x86/sev-es: Handle MWAIT/MWAITX Events
x86/sev-es: Handle MONITOR/MONITORX Events
x86/sev-es: Handle INVD Events
x86/sev-es: Handle RDPMC Events
x86/sev-es: Handle RDTSC(P) Events
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 paravirt cleanup from Ingo Molnar:
"Clean up the paravirt code after the removal of 32-bit Xen PV support"
* tag 'x86-paravirt-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/paravirt: Avoid needless paravirt step clearing page table entries
x86/paravirt: Remove set_pte_at() pv-op
x86/entry/32: Simplify CONFIG_XEN_PV build dependency
x86/paravirt: Use CONFIG_PARAVIRT_XXL instead of CONFIG_PARAVIRT
x86/paravirt: Clean up paravirt macros
x86/paravirt: Remove 32-bit support from CONFIG_PARAVIRT_XXL
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The Broadcast Assist Unit (BAU) TLB shootdown handler is being rewritten
to become the UV BAU APIC driver. It is designed to speed up sending
IPIs to selective CPUs within the system. Remove the current TLB
shutdown handler (tlb_uv.c) file and a couple of kernel hooks in the
interim.
Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Link: https://lkml.kernel.org/r/20201005203929.148656-2-mike.travis@hpe.com
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Sami reported that run_on_irqstack_cond() requires the caller to cast
functions to mismatching types, which trips indirect call Control-Flow
Integrity (CFI) in Clang.
Instead of disabling CFI on that function, provide proper helpers for
the three call variants. The actual ASM code stays the same as that is
out of reach.
[ bp: Fix __run_on_irqstack() prototype to match. ]
Fixes: 931b94145981 ("x86/entry: Provide helpers for executing on the irqstack")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Cc: <stable@vger.kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/1052
Link: https://lkml.kernel.org/r/87pn6eb5tv.fsf@nanos.tec.linutronix.de
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Add the handlers for #VC exceptions invoked at runtime.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-47-joro@8bytes.org
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The #VC handler needs special entry code because:
1. It runs on an IST stack
2. It needs to be able to handle nested #VC exceptions
To make this work, the entry code is implemented to pretend it doesn't
use an IST stack. When entered from user-mode or early SYSCALL entry
path it switches to the task stack. If entered from kernel-mode it tries
to switch back to the previous stack in the IRET frame.
The stack found in the IRET frame is validated first, and if it is not
safe to use it for the #VC handler, the code will switch to a
fall-back stack (the #VC2 IST stack). From there, it can cause nested
exceptions again.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-46-joro@8bytes.org
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With 32-bit Xen PV support gone, the following commit is not needed
anymore:
a4c0e91d1d65bc58 ("x86/entry/32: Fix XEN_PV build dependency")
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200815100641.26362-5-jgross@suse.com
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Pull KVM updates from Paolo Bonzini:
"s390:
- implement diag318
x86:
- Report last CPU for debugging
- Emulate smaller MAXPHYADDR in the guest than in the host
- .noinstr and tracing fixes from Thomas
- nested SVM page table switching optimization and fixes
Generic:
- Unify shadow MMU cache data structures across architectures"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (127 commits)
KVM: SVM: Fix sev_pin_memory() error handling
KVM: LAPIC: Set the TDCR settable bits
KVM: x86: Specify max TDP level via kvm_configure_mmu()
KVM: x86/mmu: Rename max_page_level to max_huge_page_level
KVM: x86: Dynamically calculate TDP level from max level and MAXPHYADDR
KVM: VXM: Remove temporary WARN on expected vs. actual EPTP level mismatch
KVM: x86: Pull the PGD's level from the MMU instead of recalculating it
KVM: VMX: Make vmx_load_mmu_pgd() static
KVM: x86/mmu: Add separate helper for shadow NPT root page role calc
KVM: VMX: Drop a duplicate declaration of construct_eptp()
KVM: nSVM: Correctly set the shadow NPT root level in its MMU role
KVM: Using macros instead of magic values
MIPS: KVM: Fix build error caused by 'kvm_run' cleanup
KVM: nSVM: remove nonsensical EXITINFO1 adjustment on nested NPF
KVM: x86: Add a capability for GUEST_MAXPHYADDR < HOST_MAXPHYADDR support
KVM: VMX: optimize #PF injection when MAXPHYADDR does not match
KVM: VMX: Add guest physical address check in EPT violation and misconfig
KVM: VMX: introduce vmx_need_pf_intercept
KVM: x86: update exception bitmap on CPUID changes
KVM: x86: rename update_bp_intercept to update_exception_bitmap
...
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Resolve conflicts with ongoing lockdep work that fixed the NMI entry code.
Conflicts:
arch/x86/entry/common.c
arch/x86/include/asm/idtentry.h
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Remove the temporary defines and fixup all references.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.855839271@linutronix.de
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Replace the x86 code with the generic variant. Use temporary defines for
idtentry_* which will be cleaned up in the next step.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200722220520.711492752@linutronix.de
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Cleanup the temporary defines and use irqentry_ instead of idtentry_.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.602603691@linutronix.de
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Replace the x86 variant with the generic version. Provide the relevant
architecture specific helper functions and defines.
Use a temporary define for idtentry_exit_user which will be cleaned up
seperately.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.494648601@linutronix.de
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Replace the syscall entry work handling with the generic version. Provide
the necessary helper inlines to handle the real architecture specific
parts, e.g. ptrace.
Use a temporary define for idtentry_enter_user which will be cleaned up
seperately.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.376213694@linutronix.de
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Pick up generic entry code to migrate x86 over.
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When assembling with Clang via `make LLVM_IAS=1` and CONFIG_HYPERV enabled,
we observe the following error:
<instantiation>:9:6: error: expected absolute expression
.if HYPERVISOR_REENLIGHTENMENT_VECTOR == 3
^
<instantiation>:1:1: note: while in macro instantiation
idtentry HYPERVISOR_REENLIGHTENMENT_VECTOR asm_sysvec_hyperv_reenlightenment sysvec_hyperv_reenlightenment has_error_code=0
^
./arch/x86/include/asm/idtentry.h:627:1: note: while in macro instantiation
idtentry_sysvec HYPERVISOR_REENLIGHTENMENT_VECTOR sysvec_hyperv_reenlightenment;
^
<instantiation>:9:6: error: expected absolute expression
.if HYPERVISOR_STIMER0_VECTOR == 3
^
<instantiation>:1:1: note: while in macro instantiation
idtentry HYPERVISOR_STIMER0_VECTOR asm_sysvec_hyperv_stimer0 sysvec_hyperv_stimer0 has_error_code=0
^
./arch/x86/include/asm/idtentry.h:628:1: note: while in macro instantiation
idtentry_sysvec HYPERVISOR_STIMER0_VECTOR sysvec_hyperv_stimer0;
This is caused by typos in arch/x86/include/asm/idtentry.h:
HYPERVISOR_REENLIGHTENMENT_VECTOR -> HYPERV_REENLIGHTENMENT_VECTOR
HYPERVISOR_STIMER0_VECTOR -> HYPERV_STIMER0_VECTOR
For more details see ClangBuiltLinux issue #1088.
Fixes: a16be368dd3f ("x86/entry: Convert various hypervisor vectors to IDTENTRY_SYSVEC")
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1088
Link: https://github.com/ClangBuiltLinux/linux/issues/1043
Link: https://lore.kernel.org/patchwork/patch/1272115/
Link: https://lkml.kernel.org/r/20200714194740.4548-1-sedat.dilek@gmail.com
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Clang's integrated assembler does not allow symbols with non-absolute
values to be reassigned. Modify the interrupt entry loop macro to be
compatible with IAS by using a label and an offset.
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Brian Gerst <brgerst@gmail.com>
Suggested-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Jian Cai <caij2003@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> #
Link: https://github.com/ClangBuiltLinux/linux/issues/1043
Link: https://lkml.kernel.org/r/20200714233024.1789985-1-caij2003@gmail.com
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Stack switching for interrupt handlers happens in C now for both 64 and
32bit. Remove the stale comment which claims the contrary.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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While the nmi_enter() users did
trace_hardirqs_{off_prepare,on_finish}() there was no matching
lockdep_hardirqs_*() calls to complete the picture.
Introduce idtentry_{enter,exit}_nmi() to enable proper IRQ state
tracking across the NMIs.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.216740948@infradead.org
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