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kvm: fix sorting of memslots with base_gfn == 0 

Before commit 0e60b0799f (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 0e60b0799f 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>
This commit is contained in:
Paolo Bonzini 2014-12-27 18:01:00 +01:00
parent a629df7ead
commit efbeec7098
1 changed files with 17 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
virt/kvm/kvm_main.c
View File

@ -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;