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Date: Mon, 28 Nov 2011 16:38:12 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 1.0] virtio: add and use virtio_set_features
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: agraf@suse.de, qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>

On 11/25/2011 02:23 AM, Paolo Bonzini wrote:
> On 11/24/2011 06:55 PM, Michael S. Tsirkin wrote:
>> > Could some backend make it a hard failure?
>>
>> I don't see how, there's no way to report a failure from
>> an io port write.
>
> You can exit(1), or fall back to a restricted set of features like we do for
> BAD_FEATURE. BAD_FEATURE is a special case of features that is not exposed by
> the host, but requested by the guest.
>
>> > If I understand
>> > correctly, this would have prevented the BAD_FEATURE bug too.
>>
>> Which bug?
>
> VIRTIO_F_BAD_FEATURE(30)
> This feature should never be negotiated by the guest; doing so is an indication
> that the guest is faulty. An experimental virtio PCI driver contained in Linux
> version 2.6.25 had this problem, and this feature bit can be used to detect it.
>
>> what would have prevented it.
>
> exit(1) on unsupported features.

Applied.  Thanks.

Regards,

Anthony Liguori

>
> Paolo
>
>