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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: Fri, 24 Jun 2022 19:27:39 +0000
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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>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHX7O/bKX0sOdH9/0aIlntq4rv2Q61gJw0A
- Thread-topic: [PATCH 2/2] x86/P2M: allow 2M superpage use for shadowed guests
> 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?
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?
Everything else looks good here.
> That function has been capabale of
> handling them even before commit 0ca1669871f8a ("P2M: check whether hap
> mode is enabled before using 2mb pages") disabled 2M use in this case
> for dubious reasons ("potential errors when hap is disabled").
I’m glad the days of random patches being checked in without comment or
discussion are behind us...
-George
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