Re: [PATCH] KVM: x86/vPMU: Forbid writing to MSR_F15H_PERF MSRs when guest doesn't have X86_FEATURE_PERFCTR_CORE

[Haiwei Li]

On Tue, Mar 23, 2021 at 4:48 PM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> 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@xxxxxxxxxxx>