Re: [PATCH 0/3] virtio-mmio: handle BE guests on LE hosts

Michael S. Tsirkin
2013-10-14T10:46:04Z

On Mon, Oct 14, 2013 at 10:04:55AM +0100, Pawel Moll wrote:
> On Mon, 2013-10-14 at 09:59 +0100, Michael S. Tsirkin wrote:
> > On Mon, Oct 14, 2013 at 09:24:32AM +0100, Marc Zyngier wrote:
> > > Hi Michael,
> > >
> > > On 12/10/13 19:28, Michael S. Tsirkin wrote:
> > > > On Fri, Oct 11, 2013 at 03:36:08PM +0100, Marc Zyngier wrote:
> > > >> This small patch series adds just enough kernel infrastructure and
> > > >> fixes to allow a BE guest to use virtio-mmio on a LE host, provided
> > > >> that the host actually supports such madness.
> > > >>
> > > >> This has been tested on arm64, with some fixes to KVM and a set of
> > > >> changes to kvmtool, both which I am posting separately.
> > > >>
> > > >> A branch containing all the relevant changes is at:
> > > >> git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git kvm-arm64/be-on-le-3.12-rc4
> > > >>
> > > >> Cc: Rusty Russell <rusty@rustcorp.com.au>
> > > >> Cc: Michael S. Tsirkin <mst@redhat.com>
> > > >> Cc: Pawel Moll <pawel.moll@arm.com>
> > > >
> > > > We are changing the spec to make everything LE instead of
> > > > the native endian.
> > > >
> > > > I think that'll fix the issue in a cleaner way.
> > >
> > > While I agree that it would solve the issue completely, it would also
> > > break all BE users. Is that really an option?
> >
> > I proposed several ways to create "transitional devices"
> > which can detect and switch to old interface at run-time.
> >
> > Pawel thinks that's not necessary so ...
>
> Don't wipe yourself with my name, please.
>
> You forgot to mention that the devices are versioned and the behavior of
> the legacy devices remains unchanged. No existing implementation will be
> broken.
>
> Paweł
>

I'm sorry if what I wrote was misleading.

What I meant is that under the proposed scheme, users with
existing v1 drivers must configure a v1 device explicitly.

According to the plan, drivers will be updated so they can
work with both v1 devices and new v2 devices.

But if you configure a v2 device, old drivers
will not work.

--
MST

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