Re: [PATCH] KVM: MMU: Inform users of mmio generation wraparound

[Paolo Bonzini <pbonzini@redhat.com>]

Il 20/06/2013 10:59, Takuya Yoshikawa ha scritto:
> Without this information, users will just see unexpected performance
> problems and there is little chance we will get good reports from them:
> note that mmio generation is increased even when we just start, or stop,
> dirty logging for some memory slot, in which case users should never
> expect all shadow pages to be zapped.
> 
> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> ---
>  arch/x86/kvm/mmu.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c60c5da..bc8302f 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4385,8 +4385,10 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm)
>  	 * 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 - 1))) {
> +		printk(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound");

This should at least be rate-limited, because it is guest triggerable.

But why isn't the kvm_mmu_invalidate_zap_all_pages tracepoint enough?

Paolo

>  		kvm_mmu_invalidate_zap_all_pages(kvm);
> +	}
>  }
>  
>  static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
>