linux-kernel - Re: [PATCH 2/4] KVM: SVM: use NPT page attributes

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Message-ID: <55A868F2.4040304@redhat.com>
Date:	Fri, 17 Jul 2015 04:31:14 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc:	guangrong.xiao@...ux.intel.com, jroedel@...e.de,
	alex.williamson@...hat.com, ogerlitz@...lanox.com,
	amirv@...lanox.com
Subject: Re: [PATCH 2/4] KVM: SVM: use NPT page attributes



On 17/07/2015 02:35, Andy Lutomirski wrote:
> 
>> Right now, NPT page attributes are not used, and the final page
>> attribute depends solely on gPAT (which however is not synced
>> correctly), the guest MTRRs and the guest page attributes.
>>
>> However, we can do better by mimicking what is done for VMX.
>> In the absence of PCI passthrough, the guest PAT can be ignored
>> and the page attributes can be just WB.  If passthrough is being
>> used, instead, keep respecting the guest PAT, and emulate the guest
>> MTRRs through the PAT field of the nested page tables.
>>
>> The only snag is that WP memory cannot be emulated correctly,
>> because Linux's default PAT setting only includes the other types.
>>
> 
> As of quite recently, Linux understands that the PAT has eight slots,
> and we can probably give you WP.  Do you want it?

It doesn't really matter, it's mostly used in the firmware.

Paolo
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