Re: [PATCH] arm64: Run enable method for errata work arounds on late CPUs

[Suzuki K Poulose]

On 17/01/18 13:20, Robin Murphy wrote:
> On 17/01/18 12:25, Dave Martin wrote:
> > On Wed, Jan 17, 2018 at 10:05:56AM +0000, Suzuki K Poulose wrote:
> > > When a CPU is brought up after we have finalised the system
> > > wide capabilities (i.e, features and errata), we make sure the
> > > new CPU doesn't need a new errata work around which has not been
> > > detected already. However we don't run enable() method on the new
> > > CPU for the errata work arounds already detected. This could
> > > cause the new CPU running without potential work arounds.
> > > It is upto the "enable()" method to decide if this CPU should
> > > do something about the errata.
> > >
> > > Fixes: commit 6a6efbb45b7d95c84 ("arm64: Verify CPU errata work arounds on hotplugged CPU")
> > > Cc: Will Deacon <will.deacon@xxxxxxx>
> > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > Cc: Andre Przywara <andre.przywara@xxxxxxx>
> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > Cc: Dave Martin <dave.martin@xxxxxxx>
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > > ---
> > > Â arch/arm64/kernel/cpu_errata.c | 9 ++++++---
> > > Â 1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> > > index 90a9e465339c..54e41dfe41f6 100644
> > > --- a/arch/arm64/kernel/cpu_errata.c
> > > +++ b/arch/arm64/kernel/cpu_errata.c
> > > @@ -373,15 +373,18 @@ void verify_local_cpu_errata_workarounds(void)
> > > Â {
> > > ÂÂÂÂÂ const struct arm64_cpu_capabilities *caps = arm64_errata;
> > > -ÂÂÂ for (; caps->matches; caps++)
> > > -ÂÂÂÂÂÂÂ if (!cpus_have_cap(caps->capability) &&
> > > -ÂÂÂÂÂÂÂÂÂÂÂ caps->matches(caps, SCOPE_LOCAL_CPU)) {
> > > +ÂÂÂ for (; caps->matches; caps++) {
> > > +ÂÂÂÂÂÂÂ if (cpus_have_cap(caps->capability)) {
> > > +ÂÂÂÂÂÂÂÂÂÂÂ if (caps->enable)
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ caps->enable((void *)caps);
> >
> > Do we really need this cast?
>
> Seems to me like the prototype for .enable needs updating. If any existing callback was actually using the (non-const) void* for some purpose (thankfully nothing seems to be), then passing the capability pointer into that would be unlikely to end well anyway.

I agree. This was initially written such that we could call it via on_each_cpu().
But then we later switched to stop_machine(). And we weren't using the argument until
very recently with the introduction of multiple entries for the same capability.

I will try to clean this up in a separate series, which would involve cleaning up
all the enable(), quite invasive. I would like this to go in for 4.16, as it is
needed for things like KPTI and some of the existing caps.

Cheers
Suzuki