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

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Message-ID: <55A84DD0.9040008@kernel.org>
Date:	Thu, 16 Jul 2015 17:35:28 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	Paolo Bonzini <pbonzini@...hat.com>, 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 07/07/2015 06:45 AM, Paolo Bonzini 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?

--Andy
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