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KVM: x86/pmu: Disallow emulation in the fastpath if mediated PMCs are active

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Don't handle exits in the fastpath if emulation is required, i.e. if an
instruction needs to be skipped, the mediated PMU is enabled, and one or
more PMCs is counting instructions.  With the mediated PMU, KVM's cache of
PMU state is inconsistent with respect to hardware until KVM exits the
inner run loop (when the mediated PMU is "put").

Reviewed-by: Sandipan Das <sandipan.das@amd.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-29-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-12-05 16:17:04 -08:00
parent 56bb273697
commit f7a65e58d6
2 changed files with 19 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

10
arch/x86/kvm/pmu.h
View file

@ -234,6 +234,16 @@ static inline bool pmc_is_globally_enabled(struct kvm_pmc *pmc)
return test_bit(pmc->idx, (unsigned long *)&pmu->global_ctrl);
}
static inline bool kvm_pmu_is_fastpath_emulation_allowed(struct kvm_vcpu *vcpu)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
return !kvm_vcpu_has_mediated_pmu(vcpu) ||
!bitmap_intersects(pmu->pmc_counting_instructions,
(unsigned long *)&pmu->global_ctrl,
X86_PMC_IDX_MAX);
}
void kvm_pmu_deliver_pmi(struct kvm_vcpu *vcpu);
void kvm_pmu_handle_event(struct kvm_vcpu *vcpu);
int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned pmc, u64 *data);

9
arch/x86/kvm/x86.c
View file

@ -2215,6 +2215,9 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_emulate_invd);
fastpath_t handle_fastpath_invd(struct kvm_vcpu *vcpu)
{
if (!kvm_pmu_is_fastpath_emulation_allowed(vcpu))
return EXIT_FASTPATH_NONE;
if (!kvm_emulate_invd(vcpu))
return EXIT_FASTPATH_EXIT_USERSPACE;
@ -2271,6 +2274,9 @@ static inline bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
static fastpath_t __handle_fastpath_wrmsr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
if (!kvm_pmu_is_fastpath_emulation_allowed(vcpu))
return EXIT_FASTPATH_NONE;
switch (msr) {
case APIC_BASE_MSR + (APIC_ICR >> 4):
if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(vcpu->arch.apic) ||
@ -11714,6 +11720,9 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_emulate_halt);
fastpath_t handle_fastpath_hlt(struct kvm_vcpu *vcpu)
{
if (!kvm_pmu_is_fastpath_emulation_allowed(vcpu))
return EXIT_FASTPATH_NONE;
if (!kvm_emulate_halt(vcpu))
return EXIT_FASTPATH_EXIT_USERSPACE;