Re: [Qemu-devel] [PATCH] vhost-net: Move asserts to after check for end < start

[Josh Durgin <josh.durgin@dreamhost.com>]

On 12/16/2011 12:33 PM, Bruce Rogers wrote:
> When migrating a vm using vhost-net we hit the following assertion:
>
> qemu-kvm: /usr/src/packages/BUILD/qemu-kvm-0.15.1/hw/vhost.c:30:
> vhost_dev_sync_region: Assertion `start / (0x1000 * (8 *
> sizeof(vhost_log_chunk_t)))<  dev->log_size' failed.

I consistently hit this assert while testing live migration with qemu 
1.0.1 and the master branch. Applying this patch allowed live migration 
to complete successfully. Maybe it could be reviewed and merged?

> The cases which the end<  start check is intended to catch, such as
> for vga video memory, will also likely trigger the assertion.
> Reorder the code to handle this correctly.
>
> Signed-off-by: Bruce Rogers<brogers@suse.com>
> ---
>   hw/vhost.c |    4 ++--
>   1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/vhost.c b/hw/vhost.c
> index 0870cb7..7309f71 100644
> --- a/hw/vhost.c
> +++ b/hw/vhost.c
> @@ -26,11 +26,11 @@ static void vhost_dev_sync_region(struct vhost_dev *dev,
>       vhost_log_chunk_t *to = dev->log + end / VHOST_LOG_CHUNK + 1;
>       uint64_t addr = (start / VHOST_LOG_CHUNK) * VHOST_LOG_CHUNK;
>
> -    assert(end / VHOST_LOG_CHUNK<  dev->log_size);
> -    assert(start / VHOST_LOG_CHUNK<  dev->log_size);
>       if (end<  start) {
>           return;
>       }
> +    assert(end / VHOST_LOG_CHUNK<  dev->log_size);
> +    assert(start / VHOST_LOG_CHUNK<  dev->log_size);
>       for (;from<  to; ++from) {
>           vhost_log_chunk_t log;
>           int bit;