Messages in this thread | | | Subject | Re: [PATCH V5 4/6 net-next] vhost: vhost TX zero-copy support | From | Shirley Ma <> | Date | Tue, 17 May 2011 08:22:14 -0700 |
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On Tue, 2011-05-17 at 08:55 +0300, Michael S. Tsirkin wrote: > Something in your patch that overwrites the id in vhost > and makes it put the wrong id in the used ring? > > By the way, need to keep in mind that a guest can > give us the same head twice, need to make sure this > at least does not corrupt host memory.
I think I didn't explain the problem very well here.
This patch doesn't overwrite the id. It just keeps the same coming sequence from "head return vhost_get_vq_desc()" to pass to vhost_add_used.
The same ids can be used many times once it passes to guest from vhost_add_used. There is no problem. The zero copy patch doesn't have any issue.
The problem is the order of head from return vhost_get_vq_desc should be in sequence when it passes to vhost_add_used.
The original code has no problem, because it gets one head and pass that head to vhost_add_used one by one once done the copy. So it's in sequence.
This issue can easily recreate without zerocopy patch by simply changing the order from "head return vhost_get_vq_desc" when passing to vhost_add_used.
Thanks Shirley
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