From efbeec7098eee2b3d2359d0cc24bbba0436e7f21 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Sat, 27 Dec 2014 18:01:00 +0100 Subject: [PATCH] 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 Reported-by: Andy Lutomirski Tested-by: Jamie Heilman Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f5283438ee05..050974c051b5 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;