KVM: Restrict non-existing slot state transitions
The API documentation states:
When changing an existing slot, it may be moved in the guest
physical memory space, or its flags may be modified.
An "existing slot" requires a non-zero npages (memory_size). The only
transition we should therefore allow for a non-existing slot should be
to create the slot, which includes setting a non-zero memory_size. We
currently allow calls to modify non-existing slots, which is pointless,
confusing, and possibly wrong.
With this we know that the invalidation path of __kvm_set_memory_region
is always for a delete or move and never for adding a zero size slot.
Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1cd693a..3caf816 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -758,10 +758,15 @@
new.npages = npages;
new.flags = mem->flags;
- /* Disallow changing a memory slot's size. */
+ /*
+ * Disallow changing a memory slot's size or changing anything about
+ * zero sized slots that doesn't involve making them non-zero.
+ */
r = -EINVAL;
if (npages && old.npages && npages != old.npages)
goto out_free;
+ if (!npages && !old.npages)
+ goto out_free;
/* Check for overlaps */
r = -EEXIST;
@@ -780,7 +785,7 @@
r = -ENOMEM;
/* Allocate if a slot is being created */
- if (npages && !old.npages) {
+ if (!old.npages) {
new.user_alloc = user_alloc;
new.userspace_addr = mem->userspace_addr;