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authorPaolo Bonzini <pbonzini@redhat.com>2014-12-27 18:01:00 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2014-12-28 10:01:17 +0100
commitefbeec7098eee2b3d2359d0cc24bbba0436e7f21 (patch)
tree6b90f8b272f263d093b2f40a3aa471030616bbe1
parenta629df7eadffb03e6ce4a8616e62ea29fdf69b6b (diff)
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kvm: fix sorting of memslots with base_gfn == 0
Before commit 0e60b0799fed (kvm: change memslot sorting rule from size to GFN, 2014-12-01), the memslots' sorting key was npages, meaning that a valid memslot couldn't have its sorting key equal to zero. On the other hand, a valid memslot can have base_gfn == 0, and invalid memslots are identified by base_gfn == npages == 0. Because of this, commit 0e60b0799fed broke the invariant that invalid memslots are at the end of the mslots array. When a memslot with base_gfn == 0 was created, any invalid memslot before it were left in place. This can be fixed by changing the insertion to use a ">=" comparison instead of "<=", but some care is needed to avoid breaking the case of deleting a memslot; see the comment in update_memslots. Thanks to Tiejun Chen for posting an initial patch for this bug. Reported-by: Jamie Heilman <jamie@audible.transient.net> Reported-by: Andy Lutomirski <luto@amacapital.net> Tested-by: Jamie Heilman <jamie@audible.transient.net> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--virt/kvm/kvm_main.c22
1 files changed, 17 insertions, 5 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f5283438ee0..050974c051b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -687,11 +687,23 @@ static void update_memslots(struct kvm_memslots *slots,
slots->id_to_index[mslots[i].id] = i;
i++;
}
- while (i > 0 &&
- new->base_gfn > mslots[i - 1].base_gfn) {
- mslots[i] = mslots[i - 1];
- slots->id_to_index[mslots[i].id] = i;
- i--;
+
+ /*
+ * The ">=" is needed when creating a slot with base_gfn == 0,
+ * so that it moves before all those with base_gfn == npages == 0.
+ *
+ * On the other hand, if new->npages is zero, the above loop has
+ * already left i pointing to the beginning of the empty part of
+ * mslots, and the ">=" would move the hole backwards in this
+ * case---which is wrong. So skip the loop when deleting a slot.
+ */
+ if (new->npages) {
+ while (i > 0 &&
+ new->base_gfn >= mslots[i - 1].base_gfn) {
+ mslots[i] = mslots[i - 1];
+ slots->id_to_index[mslots[i].id] = i;
+ i--;
+ }
}
mslots[i] = *new;