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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 14 Jul 2015, Ian Campbell wrote:
> 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.
 
I agree.

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