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

[Keir Fraser <keir.xen@gmail.com>]

On 30/01/2013 09:54, "Tim Deegan" <tim@xen.org> wrote:

> At 17:26 +0800 on 30 Jan (1359566815), dongxiao.xu@intel.com 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.

That's what I would expect too.

 -- Keir

> Cheers,
> 
> Tim.
> 
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