Re: [Xen-devel] [PATCH] VMX: disable SMEP feature when guest is in non-paging mode

[Tim Deegan <tim@xxxxxxx>]

At 17:26 +0800 on 30 Jan (1359566815), dongxiao.xu@xxxxxxxxx wrote:
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 4d7c93f..6347f66 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1167,6 +1167,14 @@ static void vmx_update_guest_cr(struct vcpu *v, 
> unsigned int cr)
>          {
>              v->arch.hvm_vcpu.hw_cr[4] |= X86_CR4_PSE;
>              v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_PAE;
> +            /*
> +             * SMEP is disabled if CPU is in non-paging mode in hardware.
> +             * However Xen always uses paging mode to emulate guest 
> non-paging
> +             * mode with HAP.
> +             * To emulate this behavior, SMEP needs to be manually disabled 
> when
> +             * guest switches to non-paging mode.
> +             */
> +            v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_SMEP;

Shouldn't this be handled on CR0 writes as well as CR4?  The SMEP bit of
hw_cr[4] ought to be cleared and set whenever CR0_PG is changed.

Cheers,

Tim.

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