Re: [PATCH 3/6] KVM: MMU: Add EPT support

[Anthony Liguori <anthony@codemonkey.ws>]

Yang, Sheng wrote:
> @@ -1048,17 +1071,18 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 
> *shadow_pte,
>  	 * whether the guest actually used the pte (in order to detect
>  	 * demand paging).
>  	 */
> -	spte = PT_PRESENT_MASK | PT_DIRTY_MASK;
> +	spte = shadow_base_present_pte | shadow_dirty_mask;
>  	if (!speculative)
>  		pte_access |= PT_ACCESSED_MASK;
>  	if (!dirty)
>  		pte_access &= ~ACC_WRITE_MASK;
> -	if (!(pte_access & ACC_EXEC_MASK))
> -		spte |= PT64_NX_MASK;
> -
> -	spte |= PT_PRESENT_MASK;
> +	if (pte_access & ACC_EXEC_MASK) {
> +		if (shadow_x_mask)
> +			spte |= shadow_x_mask;
> +	} else if (shadow_nx_mask)
> +		spte |= shadow_nx_mask;
>   

This looks like it may be a bug.  The old behavior sets NX if 
(pte_access & ACC_EXEC_MASK).  The new behavior unconditionally sets NX 
and never sets PRESENT.  Also, the if (shadow_x_mask) checks are 
unnecessary.  spte |= 0 is a nop.

>  	if (pte_access & ACC_USER_MASK)
> -		spte |= PT_USER_MASK;
> +		spte |= shadow_user_mask;
>  	if (largepage)
>  		spte |= PT_PAGE_SIZE_MASK;
>   

Regards,

Anthony Liguori

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