linux-kernel - Re: [PATCH] KVM/x86: pmu: Fix #GP condition check for RDPMC emulation

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Date:   Wed, 8 Jul 2020 08:18:25 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM/x86: pmu: Fix #GP condition check for RDPMC emulation

On Wed, Jul 08, 2020 at 03:44:09PM +0800, Like Xu wrote:
> in guest protected mode, if the current privilege level
> is not 0 and the pce flag in the cr4 register is cleared,
> we will inject a #gp for rdpmc usage.

Wrapping at ~58 characters is a bit aggressive.  checkpatch enforces 75
chars, something near that would be prefereable.

> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> ---
>  arch/x86/kvm/pmu.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index b86346903f2e..d080d475c808 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -372,6 +372,11 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
>  	if (!pmc)
>  		return 1;
>  
> +	if ((kvm_x86_ops.get_cpl(vcpu) != 0) &&
> +	    !(kvm_read_cr4(vcpu) & X86_CR4_PCE) &&
> +	    (kvm_read_cr4(vcpu) & X86_CR0_PE))

This reads CR4 but checks CR0.PE.

And maybe put the X86_CR4_PCE check first so that it's the focus of the
statement?

> +		return 1;
> +
>  	*data = pmc_read_counter(pmc) & mask;
>  	return 0;
>  }
> -- 
> 2.21.3
>