KVM: SEV: Treat unassigned RMP entry as benign race on PSMASH failure

When handling an RMP fault, KVM attempts to split a 2MB page via PSMASH.
If PSMASH fails, the only expected return value is FAIL_BADADDR, which does
not distinguish the reason for the bad address. Hence, another RMP entry
lookup is required to determine whether the failure was benign.

Specifically, KVM re-checks the RMP entry to determine if another CPU raced
and already smashed the entry into 4KB pages.

A concurrent operation (such as guest_memfd truncation or hole punching)
can also race and transition the page to shared, removing the page from the
RMP table and causing PSMASH to fail. This can happen even if the page is
still referenced by KVM, because guest_memfd reclaim transitions the RMP
entry to shared when the folio is removed from the page cache.

Treat an unassigned RMP entry as an expected race when re-checking after a
failed PSMASH, and skip logging an error warning.

Fixes: c63cf135cc99 ("KVM: SEV: Add support to handle RMP nested page faults")
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Link: https://patch.msgid.link/20260826-gmem-no-return-page-v4-1-3bb9c1ddb4e3@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions