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

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Wed, 2025-06-25 at 19:25 +0300, Adrian Hunter wrote:
> > To ensure I understand correctly, Am I correct in saying: movdir64b
> > clearing the integrity poison is just hardware clearing the poison
> > bit, software will still treat that page as poisoned?
> 
> Typically an integrity violation would have caused a machine check
> and the machine check handler would have marked the page
> SetPageHWPoison(page).
> 
> So we really end up with only 2 cases:
> 1. page is fine and PageHWPoison(page) is false
> 2. page may have had an integrity violation or a hardware error
> (we can't tell which), and PageHWPoison(page) is true

Could an access in userspace take an #MC, and have the kernel set the direct map
for the page to NP and kill process? Then another process with access to the
gmem fd tries to map it as private, and take a non-integrity related SEAMMODE
#MC and ends up here? It does seem safer to just avoid touching it. But I bet
there are many cases like this, and we can't check poison everywhere. 

If guestmemfd turns into more of a persistent allocator, instead of a per-VM
thing, it probably needs to do some of the checks that the page allocator does,
like poison checks.