linux-kernel - Re: [PATCH v4 05/12] KVM: x86/pmu: Error when user sets the GLOBAL

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Message-ID: <ZC9Zqn/+J5vaXKfo@google.com>
Date:   Thu, 6 Apr 2023 16:45:46 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/12] KVM: x86/pmu: Error when user sets the
 GLOBAL_STATUS reserved bits

On Tue, Feb 14, 2023, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> If the user space sets reserved bits when restoring the MSR_CORE_
> PERF_GLOBAL_STATUS register, these bits will be accidentally returned
> when the guest runs a read access to this register, and cannot be cleared
> up inside the guest, which makes the guest's PMI handler very confused.

The changelog needs to state what the patch actually does.

> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/kvm/vmx/pmu_intel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 904f832fc55d..aaea25d2cae8 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -397,7 +397,7 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  			reprogram_fixed_counters(pmu, data);
>  		break;
>  	case MSR_CORE_PERF_GLOBAL_STATUS:
> -		if (!msr_info->host_initiated)
> +		if (!msr_info->host_initiated || (data & pmu->global_ovf_ctrl_mask))

This is wrong.  Bits 60:58 are reserved in IA32_PERF_GLOBAL_OVF_CTRL, but are
ASCI, CTR_FREEZE, and LBR_FREEZE respectively in MSR_CORE_PERF_GLOBAL_STATUS.

>  			return 1; /* RO MSR */
>  
>  		pmu->global_status = data;
> -- 
> 2.39.1
>