Re: [Xen-devel] [PATCH] xen/arm: Blacklist PMU with "arm, cortex-a53-pmu"

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 15/04/2019 09:41, Andre Przywara wrote:
> On Mon, 15 Apr 2019 13:41:41 +0530
> Amit Tomer <amittomer25@xxxxxxxxx> wrote:
>
> > Hello,
> >
> > > After talking via IRC, the problem is PPIs, that this platform uses for
> > > PMU interrupts. When Xen tries to setup the IRQ forwarding for Dom0 for
> > > this device, it fails because it only supports forwarding SPIs.
> > > So interestingly we erroneously forwarded A53 PMUs (those that are
> > > described by that particular compatible string only) to Dom0 for quite a
> > > while, but nobody noticed (or cared).
> > >
> > > Amit, please adjust the commit message accordingly.
> > >   
> > Ok but original commit "d45e9b7c53428a2aa4d067927e7ef5e30783fb8b" that blacklist
> > PMU's clearly states that issue is due to PPI and that can not be
> > routed to guest.
> >
> > I thought, This patch is just continuation of same.
> Sure, but Julien was asking for a reason for this patch in the commit
> message. There are quite some platforms which use this compatible string
> already, and none of them failed so far. This is because they use SPIs,
> but as the original commit message mentions there are more issues than just
> the IRQs.
>
> All this should be in the commit message. As you have seen yourself in Ian's
> commit, it's quite helpful later on.
>
> So you should mention:
> a) the problem you encountered: PPI forwarding denied on iMX8
> b) the reason for the problem: A53 PMU not blacklisted
> c) the fix: adding the A53 compatible string to the blacklist
There are ~25 compatible string for the PMUs and I would rather not want to see 
all of them added in Xen.
From the test on Juno (it is using arm,cortex-a53-pmu with SPIs), Linux will 
happily give up because we craft the PMU registers to expose nothing.
Could we instead try to automatically blacklist any device using PPI?

Cheers,

--
Julien Grall

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