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Date: Thu, 9 May 2013 11:44:18 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20130509084418.GB32074@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] Vring: vring's listener's priority
 should higher than kvm
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To: Liu Ping Fan <qemulist@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Anthony Liguori <anthony@codemonkey.ws>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

On Thu, May 09, 2013 at 08:40:21AM +0800, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> 
> Hosts threads which handle vring should have high MemoryListener priority
> than kvm. For currently code, take the following scenario:
>   kvm_region_add() run earlier before vhost_region_add(), then in guest,
> vring's desc[i] can refer to addressX in the new region known by guest.
> But vhost does not know this new region yet, and the vring handler will
> fail.
> 
> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>

Is this seen in testing, or are you describing a theorecitical
scenario? Please make this clear in the commit log.

> ---
>  hw/virtio/dataplane/hostmem.c |    2 +-
>  hw/virtio/vhost.c             |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/dataplane/hostmem.c b/hw/virtio/dataplane/hostmem.c
> index 37292ff..67cbce1 100644
> --- a/hw/virtio/dataplane/hostmem.c
> +++ b/hw/virtio/dataplane/hostmem.c
> @@ -158,7 +158,7 @@ void hostmem_init(HostMem *hostmem)
>          .eventfd_del = hostmem_listener_eventfd_dummy,
>          .coalesced_mmio_add = hostmem_listener_coalesced_mmio_dummy,
>          .coalesced_mmio_del = hostmem_listener_coalesced_mmio_dummy,
> -        .priority = 10,
> +        .priority = 9,
>      };
>  
>      memory_listener_register(&hostmem->listener, &address_space_memory);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index fbabf99..91c313b 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -856,7 +856,7 @@ int vhost_dev_init(struct vhost_dev *hdev, int devfd, const char *devpath,
>          .log_global_stop = vhost_log_global_stop,
>          .eventfd_add = vhost_eventfd_add,
>          .eventfd_del = vhost_eventfd_del,
> -        .priority = 10
> +        .priority = 9
>      };
>      hdev->mem = g_malloc0(offsetof(struct vhost_memory, regions));
>      hdev->n_mem_sections = 0;
> -- 
> 1.7.4.4