Merge tag 'kvm-x86-fixes-6.18-rc2' of https://github.com/kvm-x86/linux into HEAD

KVM x86 fixes for 6.18:

 - Expand the KVM_PRE_FAULT_MEMORY selftest to add a regression test for the
   bug fixed by commit 3ccbf6f47098 ("KVM: x86/mmu: Return -EAGAIN if userspace
   deletes/moves memslot during prefault")

 - Don't try to get PMU capabbilities from perf when running a CPU with hybrid
   CPUs/PMUs, as perf will rightly WARN.

 - Rework KVM_CAP_GUEST_MEMFD_MMAP (newly introduced in 6.18) into a more
   generic KVM_CAP_GUEST_MEMFD_FLAGS

 - Add a guest_memfd INIT_SHARED flag and require userspace to explicitly set
   said flag to initialize memory as SHARED, irrespective of MMAP.  The
   behavior merged in 6.18 is that enabling mmap() implicitly initializes
   memory as SHARED, which would result in an ABI collision for x86 CoCo VMs
   as their memory is currently always initialized PRIVATE.

 - Allow mmap() on guest_memfd for x86 CoCo VMs, i.e. on VMs with private
   memory, to enable testing such setups, i.e. to hopefully flush out any
   other lurking ABI issues before 6.18 is officially released.

 - Add testcases to the guest_memfd selftest to cover guest_memfd without MMAP,
   and host userspace accesses to mmap()'d private memory.

1 files changed, 114 insertions, 17 deletions

diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c
index 0350a8896a2f..f04768c1d2e4 100644
--- a/tools/testing/selftests/kvm/pre_fault_memory_test.c
+++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c
@@ -10,6 +10,7 @@
 #include <test_util.h>
 #include <kvm_util.h>
 #include <processor.h>
+#include <pthread.h>
 
 /* Arbitrarily chosen values */
 #define TEST_SIZE		(SZ_2M + PAGE_SIZE)
@@ -30,18 +31,66 @@ static void guest_code(uint64_t base_gpa)
 	GUEST_DONE();
 }
 
-static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 gpa, u64 size,
-			     u64 left)
+struct slot_worker_data {
+	struct kvm_vm *vm;
+	u64 gpa;
+	uint32_t flags;
+	bool worker_ready;
+	bool prefault_ready;
+	bool recreate_slot;
+};
+
+static void *delete_slot_worker(void *__data)
+{
+	struct slot_worker_data *data = __data;
+	struct kvm_vm *vm = data->vm;
+
+	WRITE_ONCE(data->worker_ready, true);
+
+	while (!READ_ONCE(data->prefault_ready))
+		cpu_relax();
+
+	vm_mem_region_delete(vm, TEST_SLOT);
+
+	while (!READ_ONCE(data->recreate_slot))
+		cpu_relax();
+
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, data->gpa,
+				    TEST_SLOT, TEST_NPAGES, data->flags);
+
+	return NULL;
+}
+
+static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
+			     u64 size, u64 expected_left, bool private)
 {
 	struct kvm_pre_fault_memory range = {
-		.gpa = gpa,
+		.gpa = base_gpa + offset,
 		.size = size,
 		.flags = 0,
 	};
-	u64 prev;
+	struct slot_worker_data data = {
+		.vm = vcpu->vm,
+		.gpa = base_gpa,
+		.flags = private ? KVM_MEM_GUEST_MEMFD : 0,
+	};
+	bool slot_recreated = false;
+	pthread_t slot_worker;
 	int ret, save_errno;
+	u64 prev;
+
+	/*
+	 * Concurrently delete (and recreate) the slot to test KVM's handling
+	 * of a racing memslot deletion with prefaulting.
+	 */
+	pthread_create(&slot_worker, NULL, delete_slot_worker, &data);
 
-	do {
+	while (!READ_ONCE(data.worker_ready))
+		cpu_relax();
+
+	WRITE_ONCE(data.prefault_ready, true);
+
+	for (;;) {
 		prev = range.size;
 		ret = __vcpu_ioctl(vcpu, KVM_PRE_FAULT_MEMORY, &range);
 		save_errno = errno;
@@ -49,18 +98,65 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 gpa, u64 size,
 			    "%sexpecting range.size to change on %s",
 			    ret < 0 ? "not " : "",
 			    ret < 0 ? "failure" : "success");
-	} while (ret >= 0 ? range.size : save_errno == EINTR);
 
-	TEST_ASSERT(range.size == left,
-		    "Completed with %lld bytes left, expected %" PRId64,
-		    range.size, left);
+		/*
+		 * Immediately retry prefaulting if KVM was interrupted by an
+		 * unrelated signal/event.
+		 */
+		if (ret < 0 && save_errno == EINTR)
+			continue;
+
+		/*
+		 * Tell the worker to recreate the slot in order to complete
+		 * prefaulting (if prefault didn't already succeed before the
+		 * slot was deleted) and/or to prepare for the next testcase.
+		 * Wait for the worker to exit so that the next invocation of
+		 * prefaulting is guaranteed to complete (assuming no KVM bugs).
+		 */
+		if (!slot_recreated) {
+			WRITE_ONCE(data.recreate_slot, true);
+			pthread_join(slot_worker, NULL);
+			slot_recreated = true;
+
+			/*
+			 * Retry prefaulting to get a stable result, i.e. to
+			 * avoid seeing random EAGAIN failures.  Don't retry if
+			 * prefaulting already succeeded, as KVM disallows
+			 * prefaulting with size=0, i.e. blindly retrying would
+			 * result in test failures due to EINVAL.  KVM should
+			 * always return success if all bytes are prefaulted,
+			 * i.e. there is no need to guard against EAGAIN being
+			 * returned.
+			 */
+			if (range.size)
+				continue;
+		}
+
+		/*
+		 * All done if there are no remaining bytes to prefault, or if
+		 * prefaulting failed (EINTR was handled above, and EAGAIN due
+		 * to prefaulting a memslot that's being actively deleted should
+		 * be impossible since the memslot has already been recreated).
+		 */
+		if (!range.size || ret < 0)
+			break;
+	}
 
-	if (left == 0)
-		__TEST_ASSERT_VM_VCPU_IOCTL(!ret, "KVM_PRE_FAULT_MEMORY", ret, vcpu->vm);
+	TEST_ASSERT(range.size == expected_left,
+		    "Completed with %llu bytes left, expected %lu",
+		    range.size, expected_left);
+
+	/*
+	 * Assert success if prefaulting the entire range should succeed, i.e.
+	 * complete with no bytes remaining.  Otherwise prefaulting should have
+	 * failed due to ENOENT (due to RET_PF_EMULATE for emulated MMIO when
+	 * no memslot exists).
+	 */
+	if (!expected_left)
+		TEST_ASSERT_VM_VCPU_IOCTL(!ret, KVM_PRE_FAULT_MEMORY, ret, vcpu->vm);
 	else
-		/* No memory slot causes RET_PF_EMULATE. it results in -ENOENT. */
-		__TEST_ASSERT_VM_VCPU_IOCTL(ret && save_errno == ENOENT,
-					    "KVM_PRE_FAULT_MEMORY", ret, vcpu->vm);
+		TEST_ASSERT_VM_VCPU_IOCTL(ret && save_errno == ENOENT,
+					  KVM_PRE_FAULT_MEMORY, ret, vcpu->vm);
 }
 
 static void __test_pre_fault_memory(unsigned long vm_type, bool private)
@@ -97,9 +193,10 @@ static void __test_pre_fault_memory(unsigned long vm_type, bool private)
 
 	if (private)
 		vm_mem_set_private(vm, guest_test_phys_mem, TEST_SIZE);
-	pre_fault_memory(vcpu, guest_test_phys_mem, SZ_2M, 0);
-	pre_fault_memory(vcpu, guest_test_phys_mem + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
-	pre_fault_memory(vcpu, guest_test_phys_mem + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
+
+	pre_fault_memory(vcpu, guest_test_phys_mem, 0, SZ_2M, 0, private);
+	pre_fault_memory(vcpu, guest_test_phys_mem, SZ_2M, PAGE_SIZE * 2, PAGE_SIZE, private);
+	pre_fault_memory(vcpu, guest_test_phys_mem, TEST_SIZE, PAGE_SIZE, PAGE_SIZE, private);
 
 	vcpu_args_set(vcpu, 1, guest_test_virt_mem);
 	vcpu_run(vcpu);