Re: [PATCH] KVM: x86/pmu: Fix reserved bits for AMD PerfEvtSeln register

[Jim Mattson]

On Thu, Nov 18, 2021 at 5:03 AM Like Xu <like.xu.linux@xxxxxxxxx> wrote:
>
> From: Like Xu <likexu@xxxxxxxxxxx>
>
> If we run the following perf command in an AMD Milan guest:
>
>   perf stat \
>   -e cpu/event=0x1d0/ \
>   -e cpu/event=0x1c7/ \
>   -e cpu/umask=0x1f,event=0x18e/ \
>   -e cpu/umask=0x7,event=0x18e/ \
>   -e cpu/umask=0x18,event=0x18e/ \
>   ./workload
>
> dmesg will report a #GP warning from an unchecked MSR access
> error on MSR_F15H_PERF_CTLx.
>
> This is because according to APM (Revision: 4.03) Figure 13-7,
> the bits [35:32] of AMD PerfEvtSeln register is a part of the
> event select encoding, which extends the EVENT_SELECT field
> from 8 bits to 12 bits.
>
> Opportunistically update pmu->reserved_bits for reserved bit 19.
>
> Reported-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Fixes: ca724305a2b0 ("KVM: x86/vPMU: Implement AMD vPMU code for KVM")
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> index 871c426ec389..b4095dfeeee6 100644
> --- a/arch/x86/kvm/svm/pmu.c
> +++ b/arch/x86/kvm/svm/pmu.c
> @@ -281,7 +281,7 @@ static void amd_pmu_refresh(struct kvm_vcpu *vcpu)
>                 pmu->nr_arch_gp_counters = AMD64_NUM_COUNTERS;
>
>         pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << 48) - 1;
> -       pmu->reserved_bits = 0xffffffff00200000ull;
> +       pmu->reserved_bits = 0xfffffff000280000ull;

Bits 40 and 41 are guest mode and host mode. They cannot be reserved
if the guest supports nested SVM.

>         pmu->version = 1;
>         /* not applicable to AMD; but clean them to prevent any fall out */
>         pmu->counter_bitmask[KVM_PMC_FIXED] = 0;
> --
> 2.33.1
>