linux-kernel - Re: [PATCH v2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu

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Date:	Mon, 2 May 2016 15:45:46 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Bruce Rogers <brogers@...e.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	namit@...technion.ac.il, stable@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: fix ordering of cr0 initialization code in
 vmx_cpu_reset

2016-04-28 14:49-0600, Bruce Rogers:
> Commit d28bc9dd25ce reversed the order of two lines which initialize cr0,
> allowing the current (old) cr0 value to mess up vcpu initialization.
> This was observed in the checks for cr0 X86_CR0_WP bit in the context of
> kvm_mmu_reset_context(). Besides, setting vcpu->arch.cr0 after vmx_set_cr0()
> is completely redundant. Change the order back to ensure proper vcpu
> initialization.
> 
> The combination of booting with ovmf firmware when guest vcpus > 1 and kvm's
> ept=N option being set results in a VM-entry failure. This patch fixes that.
> 
> Fixes: d28bc9dd25ce ("KVM: x86: INIT and reset sequences are different")
> Cc: stable@...r.kernel.org
> Signed-off-by: Bruce Rogers <brogers@...e.com>
> ---

Queued, thanks.

>  arch/x86/kvm/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ee1c8a9..ab4a387 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5046,8 +5046,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  		vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
>  
>  	cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
> -	vmx_set_cr0(vcpu, cr0); /* enter rmode */
>  	vmx->vcpu.arch.cr0 = cr0;
> +	vmx_set_cr0(vcpu, cr0); /* enter rmode */
>  	vmx_set_cr4(vcpu, 0);
>  	vmx_set_efer(vcpu, 0);
>  	vmx_fpu_activate(vcpu);
> -- 
> 1.9.0
> 
> --
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