From: Bandan Das <bsd@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, guangrong.xiao@linux.intel.com,
kernellwp@gmail.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors
Date: Thu, 14 Jul 2016 14:52:32 -0400 [thread overview]
Message-ID: <jpgoa60jbm7.fsf@linux.bootlegged.copy> (raw)
In-Reply-To: <5951c0e5-4c41-4817-034a-5214a10cf53c@redhat.com> (Paolo Bonzini's message of "Thu, 14 Jul 2016 20:29:25 +0200")
Paolo Bonzini <pbonzini@redhat.com> writes:
> On 14/07/2016 19:38, Bandan Das wrote:
>> Paolo Bonzini <pbonzini@redhat.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. :)
Ah, thank you!
>>> 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.
Yeah... Let me rephrase, is_shadow_present_pte works because the assumption
is that both of the bits are in the first 32 bits :) You proved me wrong though,
this assumption does not mean a BUILD_BUG for the equal condition is required here.
Bandan
> Paolo
prev parent reply other threads:[~2016-07-14 18:52 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-12 22:18 [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors Bandan Das
2016-07-12 22:18 ` [PATCH v2 1/5] mmu: extend the is_present check to 32 bits Bandan Das
2016-09-01 14:20 ` Li, Liang Z
2016-09-01 15:16 ` Paolo Bonzini
2016-07-12 22:18 ` [PATCH v2 2/5] mmu: don't set the present bit unconditionally Bandan Das
2016-07-13 8:10 ` Paolo Bonzini
2016-07-12 22:18 ` [PATCH v2 3/5] mmu: remove is_present_gpte() Bandan Das
2016-07-12 22:18 ` [PATCH v2 4/5] mmu: change unconditional setting of the u bit in fault bitmap Bandan Das
2016-07-13 8:23 ` Paolo Bonzini
2016-07-13 9:06 ` Paolo Bonzini
2016-07-12 22:18 ` [PATCH v2 5/5] vmx: advertise support for ept execute only Bandan Das
2016-07-13 9:20 ` [PATCH v2 0/5] Add support for EPT execute only for nested hypervisors Paolo Bonzini
2016-07-13 9:49 ` Fam Zheng
2016-07-13 10:03 ` Paolo Bonzini
2016-07-13 15:06 ` Bandan Das
2016-07-13 15:27 ` Paolo Bonzini
2016-07-13 15:47 ` Bandan Das
2016-07-14 6:56 ` Paolo Bonzini
2016-07-14 17:38 ` Bandan Das
2016-07-14 18:29 ` Paolo Bonzini
2016-07-14 18:52 ` Bandan Das [this message]
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