KVM: SEV: Drop page refcount early during RMP fault handling

Rework KVM's handling of RMP faults to rely on MMU invalidation logic for
safety, instead of the current approach of holding onto a folio reference
until the RMP operations are complete.  I.e. drop the reference gifted by
guest_memfd immediately after getting the PFN, and instead do RMP updates
under mmu_lock, after checking for relevant MMU invalidations.

This will allow dropping guest_memfd's reference gifting entirely, which is
ideally how KVM would operate for all "follow PFN" operations (GUP has many
more complications, which is why KVM holds a reference across page
faults *on top* of the standard MMU invalidation logic).

Reviewed-by: Michael Roth <michael.roth@amd.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Link: https://patch.msgid.link/20260826-gmem-no-return-page-v4-2-3bb9c1ddb4e3@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions