From fa30b0dc91c815b9579d6f758437c35db059f5ae Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 4 Apr 2024 13:25:19 -0400
Subject: [PATCH] KVM: guest_memfd: limit overzealous WARN
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>
---
virt/kvm/guest_memfd.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index c27828b0d42d4..fd32288d0fbc4 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -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;
}
--
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