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Date: Tue, 29 Sep 2009 12:24:00 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config
	breakage
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To: Avi Kivity <avi@redhat.com>
Cc: john cooper <john.cooper@third-harmonic.com>, "Michael S. Tsirkin" <mst@redhat.com>, john cooper <john.cooper@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, Vadim Rozenfeld <vrozenfe@redhat.com>, jens.axboe@oracle.com

Avi Kivity wrote:
> On 09/29/2009 03:51 PM, Anthony Liguori wrote:
>>> The change this patch implements is passing of the
>>> identify data through a mapping established by
>>> PCI BAR #5 rather than the PCI config area, the
>>> latter of which resulted in the above breakage.
>>
>>
>> This is a massive layering violation.  The virtio-blk ABI cannot make 
>> demands of the transport.
>
> True.
>
>>
>> The better solution would be to move the entire virtio-pci config 
>> space to a separate BAR that's an MMIO region.  Then there is no 
>> practical limit on the size of the config area.
>
> Don't some fast-paths accesses go through the config space?  Using 
> mmio will slow them down.

Not that I know of.

Regards,

Anthony Liguori