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From: Marcelo Tosatti <mtosatti@redhat.com>
To: kvm <kvm@vger.kernel.org>
Cc: Gleb Natapov <gleb@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ulrich Obergfell <uobergfe@redhat.com>
Subject: KVM: MMU: make kvm_mmu_available_pages robust against n_used_mmu_pages > n_max_mmu_pages
Date: Tue, 12 Mar 2013 22:36:43 -0300	[thread overview]
Message-ID: <20130313013642.GA20722@amt.cnet> (raw)


As noticed by Ulrich Obergfell <uobergfe@redhat.com>, the mmu
counters are for beancounting purposes only - so n_used_mmu_pages and
n_max_mmu_pages could be relaxed (example: before f0f5933a1626c8df7b),
resulting in n_used_mmu_pages > n_max_mmu_pages.

Make code robust against n_used_mmu_pages > n_max_mmu_pages.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 6987108..3b1ad00 100644
--- 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)

             reply	other threads:[~2013-03-13  1:42 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-13  1:36 Marcelo Tosatti [this message]
2013-03-13  5:17 ` KVM: MMU: make kvm_mmu_available_pages robust against n_used_mmu_pages > n_max_mmu_pages Xiao Guangrong
2013-03-13  9:46 ` Gleb Natapov

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