Re: [PATCH] KVM: x86: Avoid zapping mmio sptes twice for generation wraparound

[Paolo Bonzini <pbonzini@redhat.com>]

Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto:
> Since kvm_arch_prepare_memory_region() is called right after installing
> the slot marked invalid, wraparound checking should be there to avoid
> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1.
> 
> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> ---
>  This seems to be the simplest solution for fixing the off-by-one issue
>  we discussed before.
> 
>  arch/x86/kvm/mmu.c |    5 +----
>  arch/x86/kvm/x86.c |    7 +++++++
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 0d094da..bf7af1e 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm)
>  	/*
>  	 * The very rare case: if the generation-number is round,
>  	 * zap all shadow pages.
> -	 *
> -	 * The max value is MMIO_MAX_GEN - 1 since it is not called
> -	 * when mark memslot invalid.
>  	 */
> -	if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) {
> +	if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) {
>  		printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n");
>  		kvm_mmu_invalidate_zap_all_pages(kvm);
>  	}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7d71c0f..9ddd4ff 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  		memslot->userspace_addr = userspace_addr;
>  	}
>  
> +	/*
> +	 * In these cases, slots->generation has been increased for marking the
> +	 * slot invalid, so we need wraparound checking here.
> +	 */
> +	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE))
> +		kvm_mmu_invalidate_mmio_sptes(kvm);
> +
>  	return 0;
>  }
>  
> 

Applied, thanks.

Paolo