Re: [Qemu-devel] address order of virtio-mmio devices

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Jan 29, 2015 at 08:05:50PM +0000, Peter Maydell wrote:
> On 29 January 2015 at 19:47, Laszlo Ersek <lersek@redhat.com> wrote:
> > On 01/29/15 20:12, Laszlo Ersek wrote:
> >> If the guest kernel changed its "assignment strategy" at some point, but
> >> earlier it used to match the comment (and the code), then whichever way
> >> we shape the comment will be wrong for the other kernel strategy. :) So,
> >> in that case this code is probably best left undisturbed.
> >>
> >> I'll try to dig out some kernel commit for more evidence.
> >
> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=70161ff3
> 
> Thanks for digging that up -- I was half-thinking we might
> just have got it wrong two years ago when we wrote the code :-)
> 
> We should probably update the comment to say (a) what we were
> trying to do (b) that we don't want to change it now because
> it would break existing setups.

While it is clear there is no solution that works correctly with all
kernels, I hate to think that we're going to stick with an ordering
that is clearly wrong for modern kernels, forever going forward. The
aarch64 world is only just starting out, so on balance I think we
should optimize for the future rather than the past, since that gives
right behaviour for orders of magnitude more people in the long term.

Also can we start using a versioned machine type for ARM, and make the
new machine type have the correct ordering for current kernels.

Regards,
Daniel
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