Re: [Xen-devel] Requesting for freeze exception for ARM/ITS patches

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-07-13 at 18:24 +0100, Stefano Stabellini wrote:
> On Mon, 13 Jul 2015, Wei Liu wrote:
> > On Fri, Jul 10, 2015 at 04:16:07PM +0530, Vijay Kilari wrote:
> > > Hi Wei,
> > > 
> > >     I would like to have freeze exception for ITS feature on ARM64.
> > > Design got freeze few weeks back and I have sent v4 version of patch 
> > > series
> > > today.
> > > 
> > > This patches will not impact any generic code of other platforms and have 
> > > minor
> > > changes generic arm related code. Also these patches are only for
> > > ARM64 platform.
> > > 
> > > These patches are pre-requisite for PCI support / Pass-through support
> > > on ARM64 platforms.
> > > 
> > > The risk is minor and as of today only used by Cavium ThunderX platform.
> > > 
> > 
> > 
> > I'm not a ARM expert, but last time I checked most patches in v3 are not
> > acked.
> > 
> > I also got conflict statements from maintainers and core developer. I
> > will wait a bit for them clarify the situation.
> > 
> > But as Ian said, if you can't post v4 and get most if all of your
> > patches acked / reviewed early this week, my answer to this request
> > would be no.
> 
> I pretty much agree with Ian: I went through the patches and the impact
> of the series on non-ITS platforms will be null after Vijay addresses:
> 
> - the lpi irq_desc and irq_pending allocation issues
> - improve lpi_supported to check for ITS presence
> 
> these two changes should be trivial and are certainly necessary for a
> freeze exception in my view.
> 
> 
> On this basis, if Vijay manages to resend a v5 version on time with
> those two issues covered, making sure that the new code is not enabled
> unless an its is present, then I think that a freeze exception would be
> OK as the risk would be zero.

I don't think we should be limiting ourselves to only fixing issues
which reduce the risk on non-ITS platforms. So the two issues which you
highlight above are necessary but not sufficient for a freeze exception
in my view.

For example I am firmly of the opinion that the VPLI injection code
needs to be corrected as discussed during review.

Likewise I said that care needs to be taken wrt when any of this code is
enabled, which includes not exposing it to domU even on platforms which
support ITS. I also view this as a requirement for a freeze exception.
In other words only dom0 and only on an ITS enabled system should be
exposed to any aspect of the ITS support.

Ian.


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