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

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Message-ID: <5951c0e5-4c41-4817-034a-5214a10cf53c@redhat.com>
Date:	Thu, 14 Jul 2016 20:29:25 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Bandan Das <bsd@...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



On 14/07/2016 19:38, Bandan Das wrote:
> 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 ?

I've already done it and pushed it to kvm/next. :)

>> 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.

is_shadow_present_pte() tests 0xFFFFFFFF, so it does not depend on bit 0
alone, for neither EPT nor "normal" page tables.

Paolo