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

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Message-ID: <350b8c9b-c672-d6e2-a7a9-bf7c01699a8e@redhat.com>
Date:   Thu, 18 Nov 2021 15:43:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Kim Phillips <kim.phillips@....com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/pmu: Fix reserved bits for AMD PerfEvtSeln
 register

On 11/18/21 14:03, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> 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@...gle.com>
> Fixes: ca724305a2b0 ("KVM: x86/vPMU: Implement AMD vPMU code for KVM")
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>   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;
>   	pmu->version = 1;
>   	/* not applicable to AMD; but clean them to prevent any fall out */
>   	pmu->counter_bitmask[KVM_PMC_FIXED] = 0;
> 

Queued, thanks.