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

[Dave Hansen <dave.hansen@intel.com>]

On 6/26/25 15:20, Huang, Kai wrote:
> But IMHO we may should just have a simple policy that when a page is marked
> as poisoned, it should never be touched again.  It's only one page anyway
> (for one TD) so losing that doesn't seem bad to me.  If we want to clear the
> poisoned page, then perhaps we should mark that page to be not-poisoned
> again.

The simplest policy is to do nothing.

The kernel only has 29 places that check PageHWPoison(). I'd guess that
roughly half of those are the memory-failure.c infrastructure and
bare-minimum code to handle poison, like not allowing pages to go back
into the allocator.

There are something like 5,000 lines of code in the kernel that deal
with a literal 'struct page'. 29 checks for ~5,000 sites is pretty
minuscule. We obviously don't have a policy that every place that uses
'struct page' needs to check for poison. We also don't even have a
policy where writes to or reads from a page check for poison.

Why is this TDX code so special that PageHWPoison() needs to be checked.
For instance:

$ grep -r PageHWPoison arch/x86/
arch/x86/kernel/cpu/mce/core.c:	SetPageHWPoison(p);
arch/x86/kernel/cpu/mce/core.c:	SetPageHWPoison(p);

In other words, this would be the *ONLY* arch/x86 site. Why?