linux-kernel - Re: [PATCH v3 00/16] virtio-pci: towards virtio 1.0 guest support

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Date:	Thu, 15 Jan 2015 23:32:56 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 00/16] virtio-pci: towards virtio 1.0 guest support

On Thu, Jan 15, 2015 at 10:18:18PM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > QEMU side is still undergoing polishing, but is already testable.
> 
> Looked art the qemu side for now, commenting here due to qemu patches
> not being posted to the list yet (guess that is at least partly already
> on your todo list):

Absolutely.

>  * Both legacy and modern should be switchable.  Modern needs to be
>    switchable _anyway_ for backward compatibility with old qemu
>    versions.  But legacy should be too, for testing purposes and for
>    new device types which don't need legacy in the first place.

I agree.

>  * I'd like to see some more flexibility in the pci bar layout.  Stuff
>    I have in mind:
>     - New devices which don't need a legacy bar can use bar 0 for
>       modern.
>     - One MMIO bar is enough, we can place both virtio regions and
>       msi-x regions there.  I'd suggest to add msi-x sub-regions to
>       the modern bar.

Why exactly? It seems simpler to separate things, extra BARs
have no cost.

>  * What is the reason for making the modern bar 8M in size?  Looks a bit
>    excessive, given that only 64k or so of that are actually used ...

I use a page per VQ for architectures that can locate the offset of the
accessed page that triggered EPT violation faster than the offset within
page.  I think this is the case for SVM.

> 
> virtio-scsi seems to be broken, at least my usual fedora guest didn't
> boot up from virtio-scsi disk when using a guest kernel with this patch
> series applied.
> 
> cheers,
>   Gerd

I'll re-test. Do other devices work for you? Thanks!

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