linux-kernel - Re: [PATCH 2/2] KVM: TDX: Do not clear poisoned pages

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Message-ID: <6de76911-5007-4170-bf74-e1d045c68465@intel.com>
Date: Wed, 25 Jun 2025 19:42:11 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Dave Hansen <dave.hansen@...el.com>
CC: Tony Luck <tony.luck@...el.com>, <pbonzini@...hat.com>,
	<seanjc@...gle.com>, Borislav Petkov <bp@...en8.de>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, H Peter Anvin
	<hpa@...or.com>, <linux-edac@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<kirill.shutemov@...ux.intel.com>, <kai.huang@...el.com>,
	<reinette.chatre@...el.com>, <xiaoyao.li@...el.com>,
	<tony.lindgren@...ux.intel.com>, <binbin.wu@...ux.intel.com>,
	<isaku.yamahata@...el.com>, <yan.y.zhao@...el.com>, <chao.gao@...el.com>,
	Vishal Annapurve <vannapurve@...gle.com>, <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH 2/2] KVM: TDX: Do not clear poisoned pages

On 25/06/2025 19:31, Dave Hansen wrote:
> On 6/25/25 09:25, Adrian Hunter wrote:
>>> IIUC, even if movdir64b stores contents on hwpoisoned pages, it's not
>>> going to cause any trouble.
>> No.  PageHWPoison(page) means the page should not be touched.  It must
>> be freed back to the allocator where it will never be allocated again.
> 
> What's the end-user-visible effect if the page is touched in this
> specific function in this specific way (with movdir64b)?
> 
> In other words, what does this patch do for end users?

We have another patch that clarifies that.  It turns out we need
to clear pages (MOVDIR64B) only if the platform has the so-called
partial-write errata X86_BUG_TDX_PW_MCE.

It was decided to deal with that issue separately, but maybe it
needs to bundled in the same patch set, now that the discussion
has moved in that direction?