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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-07-10 at 16:16 +0530, Vijay Kilari wrote:
>     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.

Thanks, I've been through v4 and it is certainly much improved over v3.

There are some smaller issues and one slightly more major one regarding
the mechanisms used to inject a vlpi, which I hope I've explained fully
enough in the review (in short if you do what the design draft says it
should be fixed, the incorrectness and complexity is all down to trying
to do things a different way which leads to you needing to lookup things
which you shouldn't need to lookup in places where you don't need them)

> 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.

There is some stuff which touches the non-ITS related ARM interrupt
handling, however they are mostly adding checks in is_lpi and in some
cases alternative code if it is true, which should be pretty safe.

As I mentioned during review care needs to be taken to ensure that this
code is not enabled for any guest on a platform which has no ITS and to
only enable it for dom0 on platforms which do.

Due to the structure of the patch series (which is not optimised for
being able to follow what is going on) it wasn't clear to me if this was
the case, but I think not. There are no checks for dom0 and only checks
for the presence of LPI/ITS in the physical gic, not as a property of
the individual domains.

When I say "not enabled" I mean no MMIO handlers registered, no
GITS_TRANSLATER MMIO mapping to the guest, no functional change to the
existing GIC* registers.

> These patches are pre-requisite for PCI support / Pass-through support
> on ARM64 platforms.

As I explained in my reply to Jan I think this is underselling it a
little, since AIUI it should make it possible to boot Xen on ThunderX
and do useful things (like run guests).

If you can get us a v5 with all of the issues I pointed out done _early_
next week then, with my ARM maintainers hat on, I think a freeze
exception could be something which could then be something which could
realistically be considered.

However the final call on this belongs to Wei.

Note I tried to apply this series to xen.git#staging and it had rejects,
I think it was written against #master and will need rebasing. Please
base v5 on #staging instead.

Ian.

> The risk is minor and as of today only used by Cavium ThunderX platform.
> 
> Regards
> Vijay



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