Re: [PATCH-for-10.2] vhost: Always initialize cached vring data

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 8/12/25 12:30, Hanna Czenczek wrote:
> vhost_virtqueue_start() can exit early if the descriptor ring address is
> 0, assuming the virtqueue isn’t ready to start.
> 
> In this case, all cached vring information (size, physical address,
> pointer) is left as-is.  This is OK at first startup, when that info is
> still initialized to 0, but after a reset, it will retain old (outdated)
> information.
> 
> vhost_virtqueue_start() must make sure these values are (re-)set
> properly before exiting.
> 
> (When using an IOMMU, these outdated values can stall the device:
> vhost_dev_start() deliberately produces an IOMMU miss event for each
> used vring.  If used_phys contains an outdated value, the resulting
> lookup may fail, forcing the device to be stopped.)
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
> ---
>   hw/virtio/vhost.c | 38 +++++++++++++++++++++++---------------
>   1 file changed, 23 insertions(+), 15 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>