linux-kernel - Re: [PATCH] KVM: Handle MSR_IA32_PERF

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Message-ID: <20160531145722.GA30930@potion>
Date:	Tue, 31 May 2016 16:57:22 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Dmitry Bilunov <kmeaw@...dex-team.ru>
Cc:	pbonzini@...hat.com, gsomlo@...il.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, gleb@...nel.org
Subject: Re: [PATCH] KVM: Handle MSR_IA32_PERF_CTL

2016-05-31 17:38+0300, Dmitry Bilunov:
> Intel CPUs having Turbo Boost feature implement an MSR to provide a
> control interface via rdmsr/wrmsr instructions. One could detect the
> presence of this feature by issuing one of these instructions and
> handling the #GP exception which is generated in case the referenced MSR
> is not implemented by the CPU.
> 
> KVM's vCPU model behaves exactly as a real CPU in this case by injecting
> a fault when MSR_IA32_PERF_CTL is called (which KVM does not support).
> However, some operating systems use this register during an early boot
> stage in which their kernel is not capable of handling #GP correctly,
> causing #DP and finally a triple fault effectively resetting the vCPU.
> 
> This patch implements a dummy handler for MSR_IA32_PERF_CTL to avoid the
> crashes.
> 
> Signed-off-by: Dmitry Bilunov <kmeaw@...dex-team.ru>
> ---

Applied, thank you.

>  arch/x86/kvm/x86.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c805cf4..d0a5b4b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2314,6 +2314,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_AMD64_NB_CFG:
>  	case MSR_FAM10H_MMIO_CONF_BASE:
>  	case MSR_AMD64_BU_CFG2:
> +	case MSR_IA32_PERF_CTL:
>  		msr_info->data = 0;
>  		break;
>  	case MSR_K7_EVNTSEL0 ... MSR_K7_EVNTSEL3:
> -- 
> 2.8.2
>