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

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Message-ID: <803d857f730e205f0611ec97da449a9cf98e4ffb.camel@intel.com>
Date: Wed, 18 Jun 2025 01:22:59 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Shutemov, Kirill" <kirill.shutemov@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
CC: "Du, Fan" <fan.du@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"Huang, Kai" <kai.huang@...el.com>, "quic_eberman@...cinc.com"
	<quic_eberman@...cinc.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"david@...hat.com" <david@...hat.com>, "thomas.lendacky@....com"
	<thomas.lendacky@....com>, "vbabka@...e.cz" <vbabka@...e.cz>, "Li, Zhiquan1"
	<zhiquan1.li@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"michael.roth@....com" <michael.roth@....com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"Peng, Chao P" <chao.p.peng@...el.com>, "pbonzini@...hat.com"
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	"Miao, Jun" <jun.miao@...el.com>, "pgonda@...gle.com" <pgonda@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is
 RUNNABLE

On Tue, 2025-06-17 at 08:52 +0800, Yan Zhao wrote:
> > hopefully is just handling accepting a whole range that is not 2MB aligned.
> > But
> > I think we need to verify this more.
> Ok.

In Linux guest if a memory region is not 2MB aligned the guest will accept the
ends at 4k size. If a memory region is identical to a memslot range this will be
fine. KVM will map the ends at 4k because it won't let huge pages span a
memslot. But if several memory regions are not 2MB aligned and are covered by
one large memslot, the accept will fail on the 4k ends under this proposal. I
don't know if this is a common configuration, but to cover it in the TDX guest
may not be trivial.

So I think this will only work if guests can reasonably "merge" all of the
adjacent accepts. Or of we declare a bunch of memory/memslot layouts illegal.

Kirill, how difficult would it be for TDX Linux guest to merge all 2MB adjacent
accepts?