KVM: x86: Zero out PV features cache when the CPUID leaf is not present

Clear KVM's PV feature cache prior when processing a new guest CPUID so
that KVM doesn't keep a stale cache entry if userspace does KVM_SET_CPUID2
multiple times, once with a PV features entry, and a second time without.

Fixes: 66570e966dd9 ("kvm: x86: only provide PV features if enabled in guest's CPUID")
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20241128013424.4096668-19-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 626a243febc93e4d8e6206f8b22531006d3cdf19..1157357f499ac8587a7de66939e19f2a6ba0ca20 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -272,6 +272,8 @@ void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
 {
        struct kvm_cpuid_entry2 *best = kvm_find_kvm_cpuid_features(vcpu);
 
+       vcpu->arch.pv_cpuid.features = 0;
+
        /*
         * save the feature bitmap to avoid cpuid lookup for every PV
         * operation