Re: KVM: MMU: make kvm_mmu_available_pages robust against n_used_mmu_pages > n_max_mmu_pages

[Gleb Natapov <gleb@redhat.com>]

On Tue, Mar 12, 2013 at 10:36:43PM -0300, Marcelo Tosatti wrote:
> 
> 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>
> 
Applied, thanks.

> 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)

--
			Gleb.