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Subject[PATCH v2 01/10] kvm: Restrict non-existing slot state transitions
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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.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
virt/kvm/kvm_main.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6e8fa7e..e426704 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -753,10 +753,15 @@ int __kvm_set_memory_region(struct kvm *kvm,
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;
@@ -775,7 +780,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
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;



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