From e2b43fb25243d502ad36b07bab9de09f4b76fff9 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 1 Dec 2025 17:50:48 -0800 Subject: [PATCH] KVM: x86: Apply runtime updates to current CPUID during KVM_SET_CPUID{,2} When handling KVM_SET_CPUID{,2}, do runtime CPUID updates on the vCPU's current CPUID (and caps) prior to swapping in the incoming CPUID state so that KVM doesn't lose pending updates if the incoming CPUID is rejected, and to prevent a false failure on the equality check. Note, runtime updates are unconditionally performed on the incoming/new CPUID (and associated caps), i.e. clearing the dirty flag won't negatively affect the new CPUID. Fixes: 93da6af3ae56 ("KVM: x86: Defer runtime updates of dynamic CPUID bits until CPUID emulation") Reported-by: Igor Mammedov Closes: https://lore.kernel.org/all/20251128123202.68424a95@imammedo Cc: stable@vger.kernel.org Acked-by: Igor Mammedov Tested-by: Igor Mammedov Link: https://patch.msgid.link/20251202015049.1167490-2-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/cpuid.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 52524e0ca97f..913ffb995279 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -509,11 +509,18 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, u32 vcpu_caps[NR_KVM_CPU_CAPS]; int r; + /* + * Apply pending runtime CPUID updates to the current CPUID entries to + * avoid false positives due to mismatches on KVM-owned feature flags. + */ + if (vcpu->arch.cpuid_dynamic_bits_dirty) + kvm_update_cpuid_runtime(vcpu); + /* * Swap the existing (old) entries with the incoming (new) entries in * order to massage the new entries, e.g. to account for dynamic bits - * that KVM controls, without clobbering the current guest CPUID, which - * KVM needs to preserve in order to unwind on failure. + * that KVM controls, without losing the current guest CPUID, which KVM + * needs to preserve in order to unwind on failure. * * Similarly, save the vCPU's current cpu_caps so that the capabilities * can be updated alongside the CPUID entries when performing runtime