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From: Anthony Liguori <aliguori@us.ibm.com>
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Date: Sun, 16 Dec 2012 14:36:07 -0600
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Subject: Re: [Qemu-devel] [PATCHv2] virtio: verify that all outstanding
	buffers are flushed
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To: Paolo Bonzini <pbonzini@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> writes:

>> > We technically should save the addresses and sizes too.  It makes
>> > it a heck of a lot safer then re-reading guest memory since we do some
>> > validation on the size of the sg elements.
>> 
>> Not really.
>> 
>> The guest puts the descriptors in the ring and leaves them there until
>> the device acks.  If it changes them once they're exposed but before
>> they're acked, it can get either before or after version, and always
>> could.
>
> The problems start when the guest tries to race against QEMU and defy
> the validation.  Always using the validated version is a bit easier
> than redoing the validation after migration.

Exactly.

Regards,

Anthony Liguori

>
> Paolo