KVM: MMU: handle n_free_mmu_pages > n_alloc_mmu_pages in kvm_mmu_change_mmu_pages
kvm_mmu_change_mmu_pages mishandles the case where n_alloc_mmu_pages is
smaller then n_free_mmu_pages, by not checking if the result of
the subtraction is negative.
Its a valid condition which can happen if a large number of pages has
been recently freed.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7030b5f..49a10d0 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1407,24 +1407,25 @@
*/
void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages)
{
+ int used_pages;
+
+ used_pages = kvm->arch.n_alloc_mmu_pages - kvm->arch.n_free_mmu_pages;
+ used_pages = max(0, used_pages);
+
/*
* If we set the number of mmu pages to be smaller be than the
* number of actived pages , we must to free some mmu pages before we
* change the value
*/
- if ((kvm->arch.n_alloc_mmu_pages - kvm->arch.n_free_mmu_pages) >
- kvm_nr_mmu_pages) {
- int n_used_mmu_pages = kvm->arch.n_alloc_mmu_pages
- - kvm->arch.n_free_mmu_pages;
-
- while (n_used_mmu_pages > kvm_nr_mmu_pages) {
+ if (used_pages > kvm_nr_mmu_pages) {
+ while (used_pages > kvm_nr_mmu_pages) {
struct kvm_mmu_page *page;
page = container_of(kvm->arch.active_mmu_pages.prev,
struct kvm_mmu_page, link);
kvm_mmu_zap_page(kvm, page);
- n_used_mmu_pages--;
+ used_pages--;
}
kvm->arch.n_free_mmu_pages = 0;
}