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KVM: selftests: Add a CPUID testcase for KVM_SET_CPUID2 with runtime updates

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Add a CPUID testcase to verify that KVM allows KVM_SET_CPUID2 after (or in
conjunction with) runtime updates.  This is a regression test for the bug
introduced by commit 93da6af3ae ("KVM: x86: Defer runtime updates of
dynamic CPUID bits until CPUID emulation"), where KVM would incorrectly
reject KVM_SET_CPUID due to a not handling a pending runtime update on the
current CPUID, resulting in a false mismatch between the "old" and "new"
CPUID entries.

Link: https://lore.kernel.org/all/20251128123202.68424a95@imammedo
Link: https://patch.msgid.link/20251202015049.1167490-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-12-01 17:50:49 -08:00
parent e2b43fb252
commit 824d227324
1 changed files with 15 additions and 0 deletions
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15
tools/testing/selftests/kvm/x86/cpuid_test.c
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@ -155,6 +155,7 @@ struct kvm_cpuid2 *vcpu_alloc_cpuid(struct kvm_vm *vm, vm_vaddr_t *p_gva, struct
static void set_cpuid_after_run(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *ent;
struct kvm_sregs sregs;
int rc;
u32 eax, ebx, x;
@ -162,6 +163,20 @@ static void set_cpuid_after_run(struct kvm_vcpu *vcpu)
rc = __vcpu_set_cpuid(vcpu);
TEST_ASSERT(!rc, "Setting unmodified CPUID after KVM_RUN failed: %d", rc);
/*
* Toggle CR4 bits that affect dynamic CPUID feature flags to verify
* setting unmodified CPUID succeeds with runtime CPUID updates.
*/
vcpu_sregs_get(vcpu, &sregs);
if (kvm_cpu_has(X86_FEATURE_XSAVE))
sregs.cr4 ^= X86_CR4_OSXSAVE;
if (kvm_cpu_has(X86_FEATURE_PKU))
sregs.cr4 ^= X86_CR4_PKE;
vcpu_sregs_set(vcpu, &sregs);
rc = __vcpu_set_cpuid(vcpu);
TEST_ASSERT(!rc, "Setting unmodified CPUID after KVM_RUN failed: %d", rc);
/* Changing CPU features is forbidden */
ent = vcpu_get_cpuid_entry(vcpu, 0x7);
ebx = ent->ebx;