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Re: [PATCH 2/2] x86/P2M: allow 2M superpage use for shadowed guests
- To: George Dunlap <George.Dunlap@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 27 Jun 2022 08:33:05 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, "Tim (Xen.org)" <tim@xxxxxxx>
- Delivery-date: Mon, 27 Jun 2022 06:33:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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?
> e.g., all other accesses to the p2m in the shadow code are via
> get_gfn_[something](), which (because it’s in the p2m code) handles p2m
> superpages correctly?
Well, yes - I don't think I need to reason about generic P2M code being
super-page aware?
Jan
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