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Commit 025dbbf3 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Avi Kivity
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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: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 4b656b12

arch/x86/kvm/mmu.c

+8 −7
Original line number Diff line number Diff line
@@ -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)

{

	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;

	}