linux-kernel - Re: [PATCH] KVM: x86/vPMU: Forbid writing to MSR_F15H_PERF MSRs when guest doesn't have X86_FEATURE_PERFCTR

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Message-ID: <CAB5KdOZb1pfKC8GkFSWQxBxz_KLvmSxqbnLL7qRjgfV19jiNvA@mail.gmail.com>
Date:   Wed, 24 Mar 2021 20:23:30 +0800
From:   Haiwei Li <lihaiwei.kernel@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wei Huang <wei.huang2@....com>, Joerg Roedel <joro@...tes.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86/vPMU: Forbid writing to MSR_F15H_PERF MSRs when
 guest doesn't have X86_FEATURE_PERFCTR_CORE

On Tue, Mar 23, 2021 at 4:48 PM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> MSR_F15H_PERF_CTL0-5, MSR_F15H_PERF_CTR0-5 MSRs are only available when
> X86_FEATURE_PERFCTR_CORE CPUID bit was exposed to the guest. KVM, however,
> allows these MSRs unconditionally because kvm_pmu_is_valid_msr() ->
> amd_msr_idx_to_pmc() check always passes and because kvm_pmu_set_msr() ->
> amd_pmu_set_msr() doesn't fail.

I have tested on AMD EPYC platform with perfctr_core(`cat
/proc/cpuinfo | grep perfctr_core`).
I started a vm without `perfctr-core`(-cpu host,-perfctr-core).

Before patch :

$ rdmsr 0xc0010200
0
$ wrmsr 0xc0010200 1
$ rdmsr 0xc0010200
1

After patch:

# rdmsr 0xc0010200
0
# wrmsr 0xc0010200 1
wrmsr: CPU 0 cannot set MSR 0xc0010200 to 0x0000000000000001
# rdmsr 0xc0010200
0

So,

Tested-by: Haiwei Li <lihaiwei@...cent.com>