[PATCH v2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

[PATCH v2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

[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@vger.kernel.org
Signed-off-by: Bruce Rogers <brogers@suse.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 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

Re: [PATCH v2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

[Radim Krčmář]

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@vger.kernel.org
> Signed-off-by: Bruce Rogers <brogers@suse.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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