Re: [PATCH 1/9] pci-assign: Optionally enable 64bit BARs in guest

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 01, 2012 at 06:55:40AM -0700, Alex Williamson wrote:
> On Wed, 2012-02-01 at 11:03 +0200, Avi Kivity wrote:
> > On 01/31/2012 11:14 PM, Michael S. Tsirkin wrote:
> > > On Tue, Jan 31, 2012 at 02:08:38PM -0700, Alex Williamson wrote:
> > > > On Tue, 2012-01-31 at 15:33 +0200, Avi Kivity wrote:
> > > > > On 01/31/2012 03:21 PM, Jan Kiszka wrote:
> > > > > > On 2012-01-31 14:10, Avi Kivity wrote:
> > > > > > > On 01/31/2012 02:57 PM, Jan Kiszka wrote:
> > > > > > >>>>> Seems fine, but do we really need the option?  If it doesn't work we
> > > > > > >>>>> should treat it as an ordinary but and fix it.
> > > > > > >>>>
> > > > > > >>>> So far it's against the architecture of the emulated system: our current
> > > > > > >>>> chipset predates 64 bit PCI.
> > > > > > >>>>
> > > > > > >>>
> > > > > > >>> Then it should be enabled/disabled at the chipset level.
> > > > > > >>
> > > > > > >> Makes me wonder if we already do some filtering if the device supports
> > > > > > >> 64 bit but the next bridge does not.
> > > > > > >>
> > > > > > > 
> > > > > > > Our 440fx does support 64-bit bars, so the question doesn't arise for
> > > > > > > x86.  Instead we violate the spec.
> > > > > >
> > > > > > If you mean by "our" the 440fx-qemu, not the real 440fx. That one does
> > > > > > not even support >1GB RAM.
> > > > > 
> > > > > Yes, that's what I meant.  It also supports pci hotplug, more slots, cpu
> > > > > hotplug, etc.
> > > > 
> > > > I'll drop this patch for now, it was just something I enabled based on a
> > > > query from MST and didn't want to lose it.  Maybe we need the option in
> > > > PCI core, but I'm just turn it on and hope for the best w/o giving users
> > > > a way to disable it.  Thanks,
> > > > 
> > > > Alex
> > >
> > > The patch itself makes sense to me.
> > > Avi found some bugs in 64 bit BAR handling, let's wait till that is
> > > fixed then merge this patch.
> > 
> > The bugs are unrelated to 64-bit BARs.
> > 
> > Alex, why drop the patch?  We're far from a release, if there are indeed
> > bugs there, we'll find out.
> 
> I think maybe this should be a core pci device option so we don't have
> pci-assign.mem64 vs virtio-net-pci.64bit.  I'd like to always set the
> MEM64 bit to match hardware when registering a BAR and let PCI core
> decide whether to expose it that way.

Besides the bugs, there aren't any reasons not to expose it
that way, right?

>  Besides, it was unrelated to the
> bulk of the series.  Thanks,
> 
> Alex
> 
>