linux-kernel - Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu

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Message-Id: <A88C6B7F-2E21-4AF9-ABDE-85B91F5F516C@gmail.com>
Date:	Wed, 3 Feb 2016 15:18:03 -0800
From:	Nadav Amit <nadav.amit@...il.com>
To:	Bruce Rogers <brogers@...e.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	jan.kiszka@...mens.com, Nadav Amit <namit@...technion.ac.il>
Subject: Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

Oops.

Anyhow, I see my patch has done a similar change in init_vmcb() , so you may
want to revert it as well.

Nadav

Bruce Rogers <brogers@...e.com> wrote:

> 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
> intiialization.
> 
> Signed-off-by: Bruce Rogers <brogers@...e.com>
> ---
> 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 e2951b6..21507b4 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4993,8 +4993,8 @@ 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