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Conflicts:
arch/x86/boot/startup/sme.c
arch/x86/coco/sev/core.c
arch/x86/kernel/fpu/core.c
arch/x86/kernel/fpu/xstate.c
Semantic conflict:
arch/x86/include/asm/sev-internal.h
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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For historic reasons there are some TSC-related functions in the
<asm/msr.h> header, even though there's an <asm/tsc.h> header.
To facilitate the relocation of rdtsc{,_ordered}() from <asm/msr.h>
to <asm/tsc.h> and to eventually eliminate the inclusion of
<asm/msr.h> in <asm/tsc.h>, add an explicit <asm/msr.h> dependency
to the source files that reference definitions from <asm/msr.h>.
[ mingo: Clarified the changelog. ]
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20250501054241.1245648-1-xin@zytor.com
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The signal delivery logic was modified to always set the PKRU bit in
xregs_state->header->xfeatures by this commit:
ae6012d72fa6 ("x86/pkeys: Ensure updated PKRU value is XRSTOR'd")
However, the change derives the bitmask value using XGETBV(1), rather
than simply updating the buffer that already holds the value. Thus, this
approach induces an unnecessary dependency on XGETBV1 for PKRU handling.
Eliminate the dependency by using the established helper function.
Subsequently, remove the now-unused 'mask' argument.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20250416021720.12305-9-chang.seok.bae@intel.com
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Currently, saving register states in the signal frame, the legacy feature
bits are always set in xregs_state->header->xfeatures. This code sequence
can be generalized for reuse in similar cases.
Refactor the logic to ensure a consistent approach across similar usages.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250416021720.12305-8-chang.seok.bae@intel.com
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This will make the removal of the task_struct::thread.fpu array
easier.
No change in functionality - code generated before and after this
commit is identical on x86-defconfig:
kepler:~/tip> diff -up vmlinux.before.asm vmlinux.after.asm
kepler:~/tip>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250409211127.3544993-3-mingo@kernel.org
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Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Xin Li <xin@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Tie together the %[xa] in the XSAVE/XRSTOR definitions with the
respective usage in the asm macros so that it is perfectly clear.
No functional changes.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
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Current minimum required version of binutils is 2.25, which
supports XSAVE{,OPT,C,S} and XRSTOR{,S} instruction mnemonics.
Replace the byte-wise specification of XSAVE{,OPT,C,S}
and XRSTOR{,S} with these proper mnemonics.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250313130251.383204-1-ubizjak@gmail.com
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When XSTATE_BV[i] is 0, and XRSTOR attempts to restore state component
'i' it ignores any value in the XSAVE buffer and instead restores the
state component's init value.
This means that if XSAVE writes XSTATE_BV[PKRU]=0 then XRSTOR will
ignore the value that update_pkru_in_sigframe() writes to the XSAVE buffer.
XSTATE_BV[PKRU] only gets written as 0 if PKRU is in its init state. On
Intel CPUs, basically never happens because the kernel usually
overwrites the init value (aside: this is why we didn't notice this bug
until now). But on AMD, the init tracker is more aggressive and will
track PKRU as being in its init state upon any wrpkru(0x0).
Unfortunately, sig_prepare_pkru() does just that: wrpkru(0x0).
This writes XSTATE_BV[PKRU]=0 which makes XRSTOR ignore the PKRU value
in the sigframe.
To fix this, always overwrite the sigframe XSTATE_BV with a value that
has XSTATE_BV[PKRU]==1. This ensures that XRSTOR will not ignore what
update_pkru_in_sigframe() wrote.
The problematic sequence of events is something like this:
Userspace does:
* wrpkru(0xffff0000) (or whatever)
* Hardware sets: XINUSE[PKRU]=1
Signal happens, kernel is entered:
* sig_prepare_pkru() => wrpkru(0x00000000)
* Hardware sets: XINUSE[PKRU]=0 (aggressive AMD init tracker)
* XSAVE writes most of XSAVE buffer, including
XSTATE_BV[PKRU]=XINUSE[PKRU]=0
* update_pkru_in_sigframe() overwrites PKRU in XSAVE buffer
... signal handling
* XRSTOR sees XSTATE_BV[PKRU]==0, ignores just-written value
from update_pkru_in_sigframe()
Fixes: 70044df250d0 ("x86/pkeys: Update PKRU to enable all pkeys before XSAVE")
Suggested-by: Rudi Horn <rudi.horn@oracle.com>
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20241119174520.3987538-3-aruna.ramakrishna%40oracle.com
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update_pkru_in_sigframe() will shortly need some information which
is only available inside xsave_to_user_sigframe(). Move
update_pkru_in_sigframe() inside the other function to make it
easier to provide it that information.
No functional changes.
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20241119174520.3987538-2-aruna.ramakrishna%40oracle.com
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 memory management updates from Thomas Gleixner:
- Make LAM enablement safe vs. kernel threads using a process mm
temporarily as switching back to the process would not update CR3 and
therefore not enable LAM causing faults in user space when using
tagged pointers. Cure it by synchronizing LAM enablement via IPIs to
all CPUs which use the related mm.
- Cure a LAM harmless inconsistency between CR3 and the state during
context switch. It's both confusing and prone to lead to real bugs
- Handle alt stack handling for threads which run with a non-zero
protection key. The non-zero key prevents the kernel to access the
alternate stack. Cure it by temporarily enabling all protection keys
for the alternate stack setup/restore operations.
- Provide a EFI config table identity mapping for kexec kernel to
prevent kexec fails because the new kernel cannot access the config
table array
- Use GB pages only when a full GB is mapped in the identity map as
otherwise the CPU can speculate into reserved areas after the end of
memory which causes malfunction on UV systems.
- Remove the noisy and pointless SRAT table dump during boot
- Use is_ioremap_addr() for iounmap() address range checks instead of
high_memory. is_ioremap_addr() is more precise.
* tag 'x86-mm-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/ioremap: Improve iounmap() address range checks
x86/mm: Remove duplicate check from build_cr3()
x86/mm: Remove unused NX related declarations
x86/mm: Remove unused CR3_HW_ASID_BITS
x86/mm: Don't print out SRAT table information
x86/mm/ident_map: Use gbpages only where full GB page should be mapped.
x86/kexec: Add EFI config table identity mapping for kexec kernel
selftests/mm: Add new testcases for pkeys
x86/pkeys: Restore altstack access in sigreturn()
x86/pkeys: Update PKRU to enable all pkeys before XSAVE
x86/pkeys: Add helper functions to update PKRU on the sigframe
x86/pkeys: Add PKRU as a parameter in signal handling functions
x86/mm: Cleanup prctl_enable_tagged_addr() nr_bits error checking
x86/mm: Fix LAM inconsistency during context switch
x86/mm: Use IPIs to synchronize LAM enablement
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There are two distinct CPU features related to the use of XSAVES and LBR:
whether LBR is itself supported and whether XSAVES supports LBR. The LBR
subsystem correctly checks both in intel_pmu_arch_lbr_init(), but the
XSTATE subsystem does not.
The LBR bit is only removed from xfeatures_mask_independent when LBR is not
supported by the CPU, but there is no validation of XSTATE support.
If XSAVES does not support LBR the write to IA32_XSS causes a #GP fault,
leaving the state of IA32_XSS unchanged, i.e. zero. The fault is handled
with a warning and the boot continues.
Consequently the next XRSTORS which tries to restore supervisor state fails
with #GP because the RFBM has zero for all supervisor features, which does
not match the XCOMP_BV field.
As XFEATURE_MASK_FPSTATE includes supervisor features setting up the FPU
causes a #GP, which ends up in fpu_reset_from_exception_fixup(). That fails
due to the same problem resulting in recursive #GPs until the kernel runs
out of stack space and double faults.
Prevent this by storing the supported independent features in
fpu_kernel_cfg during XSTATE initialization and use that cached value for
retrieving the independent feature bits to be written into IA32_XSS.
[ tglx: Massaged change log ]
Fixes: f0dccc9da4c0 ("x86/fpu/xstate: Support dynamic supervisor feature for LBR")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20240812-xsave-lbr-fix-v3-1-95bac1bf62f4@gmail.com
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In the case where a user thread sets up an alternate signal stack protected
by the default PKEY (i.e. PKEY 0), while the thread's stack is protected by
a non-zero PKEY, both these PKEYS have to be enabled in the PKRU register
for the signal to be delivered to the application correctly. However, the
PKRU value restored after handling the signal must not enable this extra
PKEY (i.e. PKEY 0) - i.e., the PKRU value in the sigframe has to be
overwritten with the user-defined value.
Add helper functions that will update PKRU value in the sigframe after
XSAVE.
Note that sig_prepare_pkru() makes no assumption about which PKEY could
be used to protect the altstack (i.e. it may not be part of init_pkru),
and so enables all PKEYS.
No functional change.
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240802061318.2140081-3-aruna.ramakrishna@oracle.com
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Zap the hack of using an ALTERNATIVE_3() internal label, as suggested by
bgerst:
https://lore.kernel.org/r/CAMzpN2i4oJ-Dv0qO46Fd-DxNv5z9=x%2BvO%2B8g=47NiiAf8QEJYA@mail.gmail.com
in favor of a label local to this macro only, as it should be done.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240607111701.8366-11-bp@kernel.org
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SEV-ES allows passing custom contents for x87, SSE and AVX state into the VMSA.
Allow userspace to do that with the usual KVM_SET_XSAVE API and only mark
FPU contents as confidential after it has been copied and encrypted into
the VMSA.
Since the XSAVE state for AVX is the first, it does not need the
compacted-state handling of get_xsave_addr(). However, there are other
parts of XSAVE state in the VMSA that currently are not handled, and
the validation logic of get_xsave_addr() is pointless to duplicate
in KVM, so move get_xsave_addr() to public FPU API; it is really just
a facility to operate on XSAVE state and does not expose any internal
details of arch/x86/kernel/fpu.
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240404121327.3107131-12-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Commit 672365477ae8 ("x86/fpu: Update XFD state where required") and
commit 8bf26758ca96 ("x86/fpu: Add XFD state to fpstate") introduced a
per CPU variable xfd_state to keep the MSR_IA32_XFD value cached, in
order to avoid unnecessary writes to the MSR.
On CPU hotplug MSR_IA32_XFD is reset to the init_fpstate.xfd, which
wipes out any stale state. But the per CPU cached xfd value is not
reset, which brings them out of sync.
As a consequence a subsequent xfd_update_state() might fail to update
the MSR which in turn can result in XRSTOR raising a #NM in kernel
space, which crashes the kernel.
To fix this, introduce xfd_set_state() to write xfd_state together
with MSR_IA32_XFD, and use it in all places that set MSR_IA32_XFD.
Fixes: 672365477ae8 ("x86/fpu: Update XFD state where required")
Signed-off-by: Adamos Ttofari <attofari@amazon.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240322230439.456571-1-chang.seok.bae@intel.com
Closes: https://lore.kernel.org/lkml/20230511152818.13839-1-attofari@amazon.de
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Plumb an xfeatures mask into __copy_xstate_to_uabi_buf() so that KVM can
constrain which xfeatures are saved into the userspace buffer without
having to modify the user_xfeatures field in KVM's guest_fpu state.
KVM's ABI for KVM_GET_XSAVE{2} is that features that are not exposed to
guest must not show up in the effective xstate_bv field of the buffer.
Saving only the guest-supported xfeatures allows userspace to load the
saved state on a different host with a fewer xfeatures, so long as the
target host supports the xfeatures that are exposed to the guest.
KVM currently sets user_xfeatures directly to restrict KVM_GET_XSAVE{2} to
the set of guest-supported xfeatures, but doing so broke KVM's historical
ABI for KVM_SET_XSAVE, which allows userspace to load any xfeatures that
are supported by the *host*.
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230928001956.924301-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Both KVM (through KVM_SET_XSTATE) and ptrace (through PTRACE_SETREGSET
with NT_X86_XSTATE) ultimately call copy_uabi_from_kernel_to_xstate(),
but the canonical locations for the current PKRU value for KVM guests
and processes in a ptrace stop are different (in the kvm_vcpu_arch and
the thread_state structs respectively).
In preparation for eventually handling PKRU in
copy_uabi_to_xstate, pass in a pointer to the PKRU location.
Signed-off-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20221115230932.7126-3-khuey%40kylehuey.com
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This will allow copy_sigframe_from_user_to_xstate() to grab the address of
thread_struct's pkru value in a later patch.
Signed-off-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20221115230932.7126-2-khuey%40kylehuey.com
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XSAVEC is the user space counterpart of XSAVES which cannot save supervisor
state. In virtualization scenarios the hypervisor does not expose XSAVES
but XSAVEC to the guest, though the kernel does not make use of it.
That's unfortunate because XSAVEC uses the compacted format of saving the
XSTATE. This is more efficient in terms of storage space vs. XSAVE[OPT] as
it does not create holes for XSTATE components which are not supported or
enabled by the kernel but are available in hardware. There is room for
further optimizations when XSAVEC/S and XGETBV1 are supported.
In order to support XSAVEC:
- Define the XSAVEC ASM macro as it's not yet supported by the required
minimal toolchain.
- Create a software defined X86_FEATURE_XCOMPACTED to select the compacted
XSTATE buffer format for both XSAVEC and XSAVES.
- Make XSAVEC an option in the 'XSAVE' ASM alternatives
Requested-by: Andrew Cooper <Andrew.Cooper3@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220404104820.598704095@linutronix.de
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Pull kvm updates from Paolo Bonzini:
"RISCV:
- Use common KVM implementation of MMU memory caches
- SBI v0.2 support for Guest
- Initial KVM selftests support
- Fix to avoid spurious virtual interrupts after clearing hideleg CSR
- Update email address for Anup and Atish
ARM:
- Simplification of the 'vcpu first run' by integrating it into KVM's
'pid change' flow
- Refactoring of the FP and SVE state tracking, also leading to a
simpler state and less shared data between EL1 and EL2 in the nVHE
case
- Tidy up the header file usage for the nvhe hyp object
- New HYP unsharing mechanism, finally allowing pages to be unmapped
from the Stage-1 EL2 page-tables
- Various pKVM cleanups around refcounting and sharing
- A couple of vgic fixes for bugs that would trigger once the vcpu
xarray rework is merged, but not sooner
- Add minimal support for ARMv8.7's PMU extension
- Rework kvm_pgtable initialisation ahead of the NV work
- New selftest for IRQ injection
- Teach selftests about the lack of default IPA space and page sizes
- Expand sysreg selftest to deal with Pointer Authentication
- The usual bunch of cleanups and doc update
s390:
- fix sigp sense/start/stop/inconsistency
- cleanups
x86:
- Clean up some function prototypes more
- improved gfn_to_pfn_cache with proper invalidation, used by Xen
emulation
- add KVM_IRQ_ROUTING_XEN_EVTCHN and event channel delivery
- completely remove potential TOC/TOU races in nested SVM consistency
checks
- update some PMCs on emulated instructions
- Intel AMX support (joint work between Thomas and Intel)
- large MMU cleanups
- module parameter to disable PMU virtualization
- cleanup register cache
- first part of halt handling cleanups
- Hyper-V enlightened MSR bitmap support for nested hypervisors
Generic:
- clean up Makefiles
- introduce CONFIG_HAVE_KVM_DIRTY_RING
- optimize memslot lookup using a tree
- optimize vCPU array usage by converting to xarray"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (268 commits)
x86/fpu: Fix inline prefix warnings
selftest: kvm: Add amx selftest
selftest: kvm: Move struct kvm_x86_state to header
selftest: kvm: Reorder vcpu_load_state steps for AMX
kvm: x86: Disable interception for IA32_XFD on demand
x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state()
kvm: selftests: Add support for KVM_CAP_XSAVE2
kvm: x86: Add support for getting/setting expanded xstate buffer
x86/fpu: Add uabi_size to guest_fpu
kvm: x86: Add CPUID support for Intel AMX
kvm: x86: Add XCR0 support for Intel AMX
kvm: x86: Disable RDMSR interception of IA32_XFD_ERR
kvm: x86: Emulate IA32_XFD_ERR for guest
kvm: x86: Intercept #NM for saving IA32_XFD_ERR
x86/fpu: Prepare xfd_err in struct fpu_guest
kvm: x86: Add emulation for IA32_XFD
x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation
kvm: x86: Enable dynamic xfeatures at KVM_SET_CPUID2
x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM
x86/fpu: Add guest support to xfd_enable_feature()
...
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Guest support for dynamically enabled FPU features requires a few
modifications to the enablement function which is currently invoked from
the #NM handler:
1) Use guest permissions and sizes for the update
2) Update fpu_guest state accordingly
3) Take into account that the enabling can be triggered either from a
running guest via XSETBV and MSR_IA32_XFD write emulation or from
a guest restore. In the latter case the guests fpstate is not the
current tasks active fpstate.
Split the function and implement the guest mechanics throughout the
callchain.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-7-yang.zhong@intel.com>
[Add 32-bit stub for __xfd_enable_feature. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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KVM requires a clear separation of host user space and guest permissions
for dynamic XSTATE components.
Add a guest permissions member to struct fpu and a separate set of prctl()
arguments: ARCH_GET_XCOMP_GUEST_PERM and ARCH_REQ_XCOMP_GUEST_PERM.
The semantics are equivalent to the host user space permission control
except for the following constraints:
1) Permissions have to be requested before the first vCPU is created
2) Permissions are frozen when the first vCPU is created to ensure
consistency. Any attempt to expand permissions via the prctl() after
that point is rejected.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-2-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Employ EX_TYPE_EFAULT_REG to store '-EFAULT' into the %[err] register
on exception. All the callers only ever test for 0, so the change
from -1 to -EFAULT is immaterial.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211110101325.604494664@infradead.org
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tl;dr: AMX state is ~8k. Signal frames can have space for this
~8k and each signal entry writes out all 8k even if it is zeros.
Skip writing zeros for AMX to speed up signal delivery by about
4% overall when AMX is in its init state.
This is a user-visible change to the sigframe ABI.
== Hardware XSAVE Background ==
XSAVE state components may be tracked by the processor as being
in their initial configuration. Software can detect which
features are in this configuration by looking at the XSTATE_BV
field in an XSAVE buffer or with the XGETBV(1) instruction.
Both the XSAVE and XSAVEOPT instructions enumerate features s
being in the initial configuration via the XSTATE_BV field in the
XSAVE header, However, XSAVEOPT declines to actually write
features in their initial configuration to the buffer. XSAVE
writes the feature unconditionally, regardless of whether it is
in the initial configuration or not.
Basically, XSAVE users never need to inspect XSTATE_BV to
determine if the feature has been written to the buffer.
XSAVEOPT users *do* need to inspect XSTATE_BV. They might also
need to clear out the buffer if they want to make an isolated
change to the state, like modifying one register.
== Software Signal / XSAVE Background ==
Signal frames have historically been written with XSAVE itself.
Each state is written in its entirety, regardless of being in its
initial configuration.
In other words, the signal frame ABI uses the XSAVE behavior, not
the XSAVEOPT behavior.
== Problem ==
This means that any application which has acquired permission to
use AMX via ARCH_REQ_XCOMP_PERM will write 8k of state to the
signal frame. This 8k write will occur even when AMX was in its
initial configuration and software *knows* this because of
XSTATE_BV.
This problem also exists to a lesser degree with AVX-512 and its
2k of state. However, AVX-512 use does not require
ARCH_REQ_XCOMP_PERM and is more likely to have existing users
which would be impacted by any change in behavior.
== Solution ==
Stop writing out AMX xfeatures which are in their initial state
to the signal frame. This effectively makes the signal frame
XSAVE buffer look as if it were written with a combination of
XSAVEOPT and XSAVE behavior. Userspace which handles XSAVEOPT-
style buffers should be able to handle this naturally.
For now, include only the AMX xfeatures: XTILE and XTILEDATA in
this new behavior. These require new ABI to use anyway, which
makes their users very unlikely to be broken. This XSAVEOPT-like
behavior should be expected for all future dynamic xfeatures. It
may also be extended to legacy features like AVX-512 in the
future.
Only attempt this optimization on systems with dynamic features.
Disable dynamic feature support (XFD) if XGETBV1 is unavailable
by adding a CPUID dependency.
This has been measured to reduce the *overall* cycle cost of
signal delivery by about 4%.
Fixes: 2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: "Chang S. Bae" <chang.seok.bae@intel.com>
Link: https://lore.kernel.org/r/20211102224750.FA412E26@davehans-spike.ostc.intel.com
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The IA32_XFD_MSR allows to arm #NM traps for XSTATE components which are
enabled in XCR0. The register has to be restored before the tasks XSTATE is
restored. The life time rules are the same as for FPU state.
XFD is updated on return to userspace only when the FPU state of the task
is not up to date in the registers. It's updated before the XRSTORS so
that eventually enabled dynamic features are restored as well and not
brought into init state.
Also in signal handling for restoring FPU state from user space the
correctness of the XFD state has to be ensured.
Add it to CPU initialization and resume as well.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211021225527.10184-17-chang.seok.bae@intel.com
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Add debug functionality to ensure that the XFD MSR is up to date for XSAVE*
and XRSTOR* operations.
[ tglx: Improve comment. ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-16-chang.seok.bae@intel.com
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Add storage for XFD register state to struct fpstate. This will be used to
store the XFD MSR state. This will be used for switching the XFD MSR when
FPU content is restored.
Add a per-CPU variable to cache the current MSR value so the MSR has only
to be written when the values are different.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-15-chang.seok.bae@intel.com
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Dynamically enabled XSTATE features are by default disabled for all
processes. A process has to request permission to use such a feature.
To support this implement a architecture specific prctl() with the options:
- ARCH_GET_XCOMP_SUPP
Copies the supported feature bitmap into the user space provided
u64 storage. The pointer is handed in via arg2
- ARCH_GET_XCOMP_PERM
Copies the process wide permitted feature bitmap into the user space
provided u64 storage. The pointer is handed in via arg2
- ARCH_REQ_XCOMP_PERM
Request permission for a feature set. A feature set can be mapped to a
facility, e.g. AMX, and can require one or more XSTATE components to
be enabled.
The feature argument is the number of the highest XSTATE component
which is required for a facility to work.
The request argument is not a user supplied bitmap because that makes
filtering harder (think seccomp) and even impossible because to
support 32bit tasks the argument would have to be a pointer.
The permission mechanism works this way:
Task asks for permission for a facility and kernel checks whether that's
supported. If supported it does:
1) Check whether permission has already been granted
2) Compute the size of the required kernel and user space buffer
(sigframe) size.
3) Validate that no task has a sigaltstack installed
which is smaller than the resulting sigframe size
4) Add the requested feature bit(s) to the permission bitmap of
current->group_leader->fpu and store the sizes in the group
leaders fpu struct as well.
If that is successful then the feature is still not enabled for any of the
tasks. The first usage of a related instruction will result in a #NM
trap. The trap handler validates the permission bit of the tasks group
leader and if permitted it installs a larger kernel buffer and transfers
the permission and size info to the new fpstate container which makes all
the FPU functions which require per task information aware of the extended
feature set.
[ tglx: Adopted to new base code, added missing serialization,
massaged namings, comments and changelog ]
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-7-chang.seok.bae@intel.com
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Now that everything is mopped up, move all the helpers and prototypes into
the core header. They are not required by the outside.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.514095101@linutronix.de
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Use the new kernel and user space config storage to store and retrieve the
XSTATE buffer sizes. The default and the maximum size are the same for now,
but will change when support for dynamically enabled features is added.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.296830097@linutronix.de
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Prepare for dynamically enabled states per task. The function needs to
retrieve the features and sizes which are valid in a fpstate
context. Retrieve them from fpstate.
Move the function declarations to the core header as they are not
required anywhere else.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.233529986@linutronix.de
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With dynamically enabled features the copy function must know the features
and the size which is valid for the task. Retrieve them from fpstate.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.181495492@linutronix.de
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With dynamically enabled features the sigframe code must know the features
which are enabled for the task. Get them from fpstate.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.077781448@linutronix.de
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With variable feature sets XSAVE[S] requires to know the feature set for
which the buffer is valid. Retrieve it from fpstate.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.025695590@linutronix.de
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In order to prepare for the support of dynamically enabled FPU features,
move the clearing of xstate components to the FPU core code.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20211013145322.399567049@linutronix.de
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Move the global interfaces to api.h and the rest into the core.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011539.948837194@linutronix.de
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Nothing outside the core code needs these.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011539.513368075@linutronix.de
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Prepare for replacing the KVM copy xstate to user function by extending
copy_xstate_to_uabi_buf() with a pkru argument which allows the caller to
hand in the pkru value, which is required for KVM because the guest PKRU is
not accessible via current. Fixup all callsites accordingly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011539.191902137@linutronix.de
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No point in having this duplicated all over the place with needlessly
different defines.
Provide a proper initialization function which initializes user buffers
properly and make KVM use it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011538.897664678@linutronix.de
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