Re: [PATCH v3 6/8] KVM: Fully serialize gfn=>pfn cache refresh via mutex

[Paolo Bonzini]

On 4/29/22 23:00, Sean Christopherson wrote:
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index 05cb0bcbf662..eaef31462bbe 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -157,6 +157,13 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
>   	if (page_offset + len > PAGE_SIZE)
>   		return -EINVAL;
>   
> +	/*
> +	 * If another task is refreshing the cache, wait for it to complete.
> +	 * There is no guarantee that concurrent refreshes will see the same
> +	 * gpa, memslots generation, etc..., so they must be fully serialized.
> +	 */
> +	mutex_lock(&gpc->refresh_lock);
> +
>   	write_lock_irq(&gpc->lock);
>   
>   	old_pfn = gpc->pfn;
> @@ -248,6 +255,8 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
>    out:
>   	write_unlock_irq(&gpc->lock);
>   
> +	mutex_unlock(&gpc->refresh_lock);
> +
>   	gpc_release_pfn_and_khva(kvm, old_pfn, old_khva);
>   
>   	return ret;

Does kvm_gfn_to_pfn_cache_unmap also need to take the mutex, to avoid 
the WARN_ON(gpc->valid)?

Paolo