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KVM: guest_memfd: limit overzealous WARN

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Because kvm_gmem_get_pfn() is called from the page fault path without
any of the slots_lock, filemap lock or mmu_lock taken, it is
possible for it to race with kvm_gmem_unbind().  This is not a
problem, as any PTE that is installed temporarily will be zapped
before the guest has the occasion to run.

However, it is not possible to have a complete unbind+bind
racing with the page fault, because deleting the memslot
will call synchronize_srcu_expedited() and wait for the
page fault to be resolved.  Thus, we can still warn if
the file is there and is not the one we expect.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-04-04 13:25:19 -04:00
parent 7062372377
commit fa30b0dc91
1 changed files with 2 additions and 1 deletions
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3
virt/kvm/guest_memfd.c
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@ -499,7 +499,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
gmem = file->private_data;
if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) {
if (xa_load(&gmem->bindings, index) != slot) {
WARN_ON_ONCE(xa_load(&gmem->bindings, index));
r = -EIO;
goto out_fput;
}