linux-kernel - Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages

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Message-ID: <4cbdfd3128a6dcc67df41b47336a4479a07bf1bd.camel@intel.com>
Date: Thu, 26 Jun 2025 22:19:34 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Shutemov, Kirill" <kirill.shutemov@...el.com>
CC: "quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "Du, Fan" <fan.du@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "david@...hat.com" <david@...hat.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "tabba@...gle.com" <tabba@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, "Peng, Chao P"
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	<isaku.yamahata@...el.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "Weiny, Ira"
	<ira.weiny@...el.com>, "jroedel@...e.de" <jroedel@...e.de>, "Miao, Jun"
	<jun.miao@...el.com>, "pgonda@...gle.com" <pgonda@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge
 pages

On Thu, 2025-06-26 at 18:16 +0300, Shutemov, Kirill wrote:
> > > Please see my reply to Yan, I'm hoping y'all will agree to something
> > > between option f/g instead.
> > 
> > I'm not sure about the HWPoison approach, but I'm not totally against it. My
> > bias is that all the MM concepts are tightly interlinked. If may fit
> > perfectly,
> > but every new use needs to be checked for how fits in with the other MM
> > users of
> > it. Every time I've decided a page flag was the perfect solution to my
> > problem,
> > I got informed otherwise. Let me try to flag Kirill to this discussion. He
> > might
> > have some insights.
> 
> We chatted with Rick about this.
> 
> If I understand correctly, we are discussing the situation where the TDX
> module failed to return a page to the kernel.
> 
> I think it is reasonable to use HWPoison for this case. We cannot
> guarantee that we will read back whatever we write to the page. TDX module
> has creative ways to corrupt it. 
> 
> The memory is no longer functioning as memory. It matches the definition
> of HWPoison quite closely.

ok! Lets go f/g. Unless Yan objects.