Re: [XEN PATCH v6 0/7] FF-A notifications

[Jens Wiklander <jens.wiklander@xxxxxxxxxx>]

Hi all,

On Tue, Jun 11, 2024 at 9:09 AM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> Hi Julien and Oleksii,
>
> @Oleksii: Could we consider having this serie merged for next release ?
>
> It is a feature that is in tech-preview at the moment and as such should not 
> have any
> consequences on existing system unless it is activated explicitly in the Xen 
> configuration.
>
> There are some changes in the arm common code introducing support to register 
> SGI
> interrupt handlers in drivers. As no drivers appart from FF-A is trying to 
> register such
> handlers, the risk is minimal for existing systems.
>
>
> > On 10 Jun 2024, at 22:38, Julien Grall <julien@xxxxxxx> wrote:
> >
> > Hi Bertrand,
> >
> > On 10/06/2024 16:54, Bertrand Marquis wrote:
> >> Hi Jens,
> >>> On 10 Jun 2024, at 08:53, Jens Wiklander <jens.wiklander@xxxxxxxxxx> 
> >>> wrote:
> >>>
> >>> Hi,
> >>>
> >>> This patch set adds support for FF-A notifications. We only support
> >>> global notifications, per vCPU notifications remain unsupported.
> >>>
> >>> The first three patches are further cleanup and can be merged before the
> >>> rest if desired.
> >>>
> >>> A physical SGI is used to make Xen aware of pending FF-A notifications. 
> >>> The
> >>> physical SGI is selected by the SPMC in the secure world. Since it must 
> >>> not
> >>> already be used by Xen the SPMC is in practice forced to donate one of the
> >>> secure SGIs, but that's normally not a problem. The SGI handling in Xen is
> >>> updated to support registration of handlers for SGIs that aren't 
> >>> statically
> >>> assigned, that is, SGI IDs above GIC_SGI_MAX.
> >>>
> >>> The patch "xen/arm: add and call init_tee_secondary()" provides a hook for
> >>> register the needed per-cpu interrupt handler in "xen/arm: ffa: support
> >>> notification".
> >>>
> >>> The patch "xen/arm: add and call tee_free_domain_ctx()" provides a hook 
> >>> for
> >>> later freeing of the TEE context. This hook is used in "xen/arm: ffa:
> >>> support notification" and avoids the problem with TEE context being freed
> >>> while we need to access it when handling a Schedule Receiver interrupt. It
> >>> was suggested as an alternative in [1] that the TEE context could be freed
> >>> from complete_domain_destroy().
> >>>
> >>> [1] 
> >>> https://lore.kernel.org/all/CAHUa44H4YpoxYT7e6WNH5XJFpitZQjqP9Ng4SmTy4eWhyN+F+w@xxxxxxxxxxxxxx/
> >>>
> >>> Thanks,
> >>> Jens
> >> All patches are now reviewed and/or acked so I think they can get in for 
> >> the release.
> >
> > This would need a release-ack from Oleksii (I can't seem to find already 
> > one).
>
> You are right, i do not know why in my mind we already got one.
>
> >
> > As we discussed last week, I am fine with the idea to merge the FFA patches 
> > as the feature is tech-preview. But there are some changes in the arm 
> > generic code. Do you (or Jens) have an assessment of the risk of the 
> > changes?
>
> Agree.
>
> In my view, the changes are changing the behaviour of some internal functions 
> if an interrupt handler is register for SGI but should not have any impact 
> for other kind of interrupts.
> As there was nothing before the FF-A driver registering such interrupts, the 
> risk of the changes having any impact on existing configurations not 
> activating FF-A is fairly reduced.
>
> @Jens: do you agree with my analysis.

Yes, I agree.

Cheers,
Jens