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Re: [PATCH 2/2] x86/P2M: allow 2M superpage use for shadowed guests


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: George Dunlap <George.Dunlap@xxxxxxxxxx>
  • Date: Mon, 18 Jul 2022 05:42:22 +0000
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  • Thread-topic: [PATCH 2/2] x86/P2M: allow 2M superpage use for shadowed guests



On 27 Jun 2022, at 16:33, Jan Beulich <jbeulich@xxxxxxxx> wrote:

On 24.06.2022 21:27, George Dunlap wrote:


On 9 Dec 2021, at 11:27, Jan Beulich <jbeulich@xxxxxxxx> wrote:

For guests in shadow mode the P2M table gets used only by software. The
only place where it matters whether superpages in the P2M can be dealt
with is sh_unshadow_for_p2m_change().

It’s easy to verify that this patch is doing what it claims to do; but whether it’s correct or not depends on the veracity of this claim here. Rather than me having to duplicate whatever work you did to come to this conclusion, can you briefly explain why it’s true in a way that I can easily verify?

Would

"The table is never made accessible by hardware for address translation,
and the only checks of _PAGE_PSE in P2M entries in shadow code are in
this function (all others are against guest page table entries)."

look sufficient to you?

Sorry for the delay responding to this — yes, I think this would do, thanks.

 -George

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