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KVM: MMU: handle n_free_mmu_pages > n_alloc_mmu_pages in kvm_mmu_change_mmu_pages

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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>
This commit is contained in:
Marcelo Tosatti
2009-07-22 13:05:49 -03:00
committed by Avi Kivity
parent 4b656b1202
commit 025dbbf36a
1 changed files with 8 additions and 7 deletions
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15
arch/x86/kvm/mmu.c
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@ -1407,24 +1407,25 @@ static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp)
*/ */
void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages) 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 * 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 * number of actived pages , we must to free some mmu pages before we
* change the value * change the value
*/ */
if ((kvm->arch.n_alloc_mmu_pages - kvm->arch.n_free_mmu_pages) > if (used_pages > kvm_nr_mmu_pages) {
kvm_nr_mmu_pages) { while (used_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) {
struct kvm_mmu_page *page; struct kvm_mmu_page *page;
page = container_of(kvm->arch.active_mmu_pages.prev, page = container_of(kvm->arch.active_mmu_pages.prev,
struct kvm_mmu_page, link); struct kvm_mmu_page, link);
kvm_mmu_zap_page(kvm, page); kvm_mmu_zap_page(kvm, page);
n_used_mmu_pages--; used_pages--;
} }
kvm->arch.n_free_mmu_pages = 0; kvm->arch.n_free_mmu_pages = 0;
} }