On 5/15/2025 8:43 AM, Sean Christopherson wrote:
> Again, be more precise.
>
> On Mon, Mar 24, 2025, Mingwei Zhang wrote:
>> From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>>
>> Mediated vPMU needs to intercept EVENTSELx and FIXED_CNTR_CTRL MSRs to
>> filter out guest malicious perf events. Either writing these MSRs or
>> updating event filters would call reprogram_counter() eventually. Thus
>> check if the guest event should be filtered out in reprogram_counter().
>> If so, clear corresponding EVENTSELx MSR or FIXED_CNTR_CTRL field to
>> ensure the guest event won't be really enabled at vm-entry.
>>
>> Besides, mediated vPMU intercepts the MSRs of these guest not owned
>> counters and it just needs simply to read/write from/to pmc->counter.
>>
>> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>> Co-developed-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/pmu.c | 27 +++++++++++++++++++++++++++
>> arch/x86/kvm/pmu.h | 3 +++
>> 2 files changed, 30 insertions(+)
>>
>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>> index 63143eeb5c44..e9100dc49fdc 100644
>> --- a/arch/x86/kvm/pmu.c
>> +++ b/arch/x86/kvm/pmu.c
>> @@ -305,6 +305,11 @@ static void pmc_update_sample_period(struct kvm_pmc *pmc)
>>
>> void pmc_write_counter(struct kvm_pmc *pmc, u64 val)
>> {
>> + if (kvm_mediated_pmu_enabled(pmc->vcpu)) {
>> + pmc->counter = val & pmc_bitmask(pmc);
>> + return;
>> + }
>> +
>> /*
>> * Drop any unconsumed accumulated counts, the WRMSR is a write, not a
>> * read-modify-write. Adjust the counter value so that its value is
>> @@ -455,6 +460,28 @@ static int reprogram_counter(struct kvm_pmc *pmc)
>> bool emulate_overflow;
>> u8 fixed_ctr_ctrl;
>>
>> + if (kvm_mediated_pmu_enabled(pmu_to_vcpu(pmu))) {
>> + bool allowed = check_pmu_event_filter(pmc);
>> +
>> + if (pmc_is_gp(pmc)) {
>> + if (allowed)
>> + pmc->eventsel_hw |= pmc->eventsel &
>> + ARCH_PERFMON_EVENTSEL_ENABLE;
>> + else
>> + pmc->eventsel_hw &= ~ARCH_PERFMON_EVENTSEL_ENABLE;
>> + } else {
>> + int idx = pmc->idx - KVM_FIXED_PMC_BASE_IDX;
>> +
>> + if (allowed)
>> + pmu->fixed_ctr_ctrl_hw = pmu->fixed_ctr_ctrl;
>> + else
>> + pmu->fixed_ctr_ctrl_hw &=
>> + ~intel_fixed_bits_by_idx(idx, 0xf);
>> + }
>> +
>> + return 0;
> I think it's worth adding a helper for this, as it makes things a bit more
> self-documenting in terms of when KVM needs to "reprogram" mediated PMU PMCs.
Sure. Thanks.
