[PATCH 3/3] KVM: guest_memfd: Handle errors from xa_store_range() when binding

[Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>]

From: Ackerley Tng <ackerleytng@google.com>

Unhandled errors from xa_store_range() means kvm_gmem_bind() might falsely
reporting success, leading to false assumptions in guest_memfd's lifecycle
later.

Handle these errors by checking and returning the error to the userspace.

Fixes: a7800aa80ea4d ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 virt/kvm/guest_memfd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index d203135969d13..104f0f3d6a0b3 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -648,6 +648,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 	struct inode *inode;
 	struct file *file;
 	int r = -EINVAL;
+	void *result;
 
 	BUILD_BUG_ON(sizeof(gfn_t) != sizeof(slot->gmem.pgoff));
 
@@ -688,7 +689,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 	if (kvm_gmem_supports_mmap(inode))
 		slot->flags |= KVM_MEMSLOT_GMEM_ONLY;
 
-	xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL);
+	result = xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL);
 	filemap_invalidate_unlock(inode->i_mapping);
 
 	/*
@@ -696,7 +697,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 	 * not the other way 'round.  Active bindings are invalidated if the
 	 * file is closed before memslots are destroyed.
 	 */
-	r = 0;
+	r = xa_is_err(result) ? xa_err(result) : 0;
 err:
 	fput(file);
 	return r;

-- 
2.54.0.794.g4f17f83d09-goog