KVM: MMU: make kvm_mmu_available_pages robust against n_used_mmu_page…

…s > n_max_mmu_pages As noticed by Ulrich Obergfell <[email protected]>, the mmu counters are for beancounting purposes only - so n_used_mmu_pages and n_max_mmu_pages could be relaxed (example: before f0f5933), resulting in n_used_mmu_pages > n_max_mmu_pages. Make code robust against n_used_mmu_pages > n_max_mmu_pages. Reviewed-by: Xiao Guangrong <[email protected]> Signed-off-by: Marcelo Tosatti <[email protected]> Signed-off-by: Gleb Natapov <[email protected]>
sjhung · Mar 13, 2013 · 5d21881 · 5d21881
1 parent 57f252f
commit 5d21881
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
@@ -57,8 +57,11 @@ int kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
 
 static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
 {
-	return kvm->arch.n_max_mmu_pages -
-		kvm->arch.n_used_mmu_pages;
+	if (kvm->arch.n_max_mmu_pages > kvm->arch.n_used_mmu_pages)
+		return kvm->arch.n_max_mmu_pages -
+			kvm->arch.n_used_mmu_pages;
+
+	return 0;
 }
 
 static inline void kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)