Fix guest_memfd bugs related to binding to a memslot:

 - Handle errors when inserting into guest_memfd's binding xarray, e.g. to
   do the right thing on ENOMEM.

 - Bind a memslot only once the memslot is fully prepared (because it becomes
   reachable/visible once its inserted into gmem's bindings arraxy).

Patch 4 is a related cleanup to remove a superflous WRITE_ONCE() (unwinding
the slot update on insertion failure isn't an option if the slot is observable,
i.e. if the WRITE_ONCE() is actually necessary).

v3:
 - Nullify bindings on error before dropping invalidat lock. [Sashiko x3]
 
v2:
 - https://lore.kernel.org/all/20260902182020.2615443-1-seanjc@google.com
 - Fix the binding-too-early bug. [Sashiko]
 - Explicitly zero the bindings entry on failure to ensure there are no
   partial entries. [Sashiko]

v1: https://lore.kernel.org/all/20260826165154.766699-2-seanjc@google.com

Sean Christopherson (4):
  KVM: guest_memfd: Gracefully handle xarray errors when binding a
    memslot
  KVM: Use goto to handle errors during memslot preparation
  KVM: guest_memfd: Establish memslot<=>guest_memfd bindings *after*
    memslot is ready
  KVM: guest_memfd: Drop superfluous WRITE_ONCE() when binding a memslot

 virt/kvm/guest_memfd.c | 17 ++++++++++--
 virt/kvm/kvm_main.c    | 63 +++++++++++++++++++++++++-----------------
 2 files changed, 51 insertions(+), 29 deletions(-)


base-commit: 76671054f9a1ff6abb976583cd8da37650acdc97
-- 
2.55.0.979.g7e5102b832-goog