linux-kernel - Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is RUNNABLE

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Message-ID: <d9bf81fc03cb0d92fc0956c6a49ff695d6b2d1ad.camel@intel.com>
Date: Fri, 13 Jun 2025 00:25:58 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is
 RUNNABLE

On Thu, 2025-06-12 at 17:19 -0700, Sean Christopherson wrote:
> > I think this may need a guest opt-in, so the guest can say it can handle
> > errors
> > for both smaller and larger page size matches. So it may not matter if there
> > is
> > a rare usage or not. If KVM finds the guest opts-in (how to do that TBD), it
> > can
> > start mapping at the host level. 
> 
> Hmm, clever.  That should work; requiring an updated guest kernel to get
> optimal
> performance doesn't seem too onerous.
> 
> > If KVM doesn't see the opt-in, the guest gets 4k pages.
> 
> As in, KVM doesn't even try to use hugepage mappings?  If so, this idea
> probably
> gets my vote.

Maybe an "I can handle it" accept size bit that comes in the exit qualification?

Yan, do you see any problems with that? Like if a guest passed it in some accept
and not others? Thinking about the new "unaccept" SEAMCALL...