linux-kernel - Re: [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors

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Date:	Thu, 14 Jul 2016 13:38:53 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	kvm@...r.kernel.org, guangrong.xiao@...ux.intel.com,
	kernellwp@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 13/07/2016 17:47, Bandan Das wrote:
>>>> I wanted to keep it the former way because "PT_PRESENT_MASK is equal to VMX_EPT_READABLE_MASK"
>>>> is an assumption all throughout. I wanted to use this section to catch mismatches.
>>>
>>> I think there's no such assumption anymore, actually.  Can you double
>>> check?  If there are any, that's where the BUILD_BUG_ON should be.
>> 
>> What I meant is how they are the same bit.  is_shadow_present_pte() is probably one
>> and another one is link_shadow_page() which already has a BUILD_BUG_ON().
>
> You're right about link_shadow_page()!  We probably should change the
> PT_PRESENT_MASK to shadow_present_mask there (and then readability in
> the EPT execonly case is still provided by shadow_user_mask).

Makes sense. Would you like a new version with that added or can that be a
separate patch ?

> For is_shadow_present_pte() you have removed it in patch 1 though.

Right. But the assumption is still that is_shadow_present_pte() works because
EPT_READABLE and PT_PRESENT are the same.

> Paolo