Re: [PATCH] arm64/io: Don't use WZR in writel

From: Marc Zyngier
Date: Sat Feb 23 2019 - 13:38:09 EST

On Sat, 23 Feb 2019 18:12:54 +0000,
Bjorn Andersson <bjorn.andersson@xxxxxxxxxx> wrote:
> On Mon 11 Feb 06:59 PST 2019, Marc Zyngier wrote:
> > On 11/02/2019 14:29, AngeloGioacchino Del Regno wrote:
> >
> > [...]
> >
> > > Also, just one more thing: yes this thing is going ARM64-wide and
> > > - from my findings - it's targeting certain Qualcomm SoCs, but...
> > > I'm not sure that only QC is affected by that, others may as well
> > > have the same stupid bug.
> > >
> >
> > At the moment, only QC SoCs seem to be affected, probably because
> > everyone else has debugged their hypervisor (or most likely doesn't
> > bother with shipping one).
> >
> > In all honesty, we need some information from QC here: which SoCs are
> > affected, what is the exact nature of the bug, can it be triggered from
> > EL0. Randomly papering over symptoms is not something I really like
> > doing, and is likely to generate problems on unaffected systems.
> >
> The bug at hand is that the XZR is not deemed a valid source in the
> virtualization of the SMMU registers. It was identified and fixed for
> all platforms that are shipping kernels based on v4.9 or later.

When you say "fixed": Do you mean fixed in the firmware? Or by adding
a workaround in the shipped kernel? If the former, is this part of an
official QC statement, with an associated erratum number? Is this
really limited to the SMMU accesses?

> As such Angelo's list of affected platforms covers the high-profile
> ones. In particular MSM8996 and MSM8998 is getting pretty good support
> upstream, if we can figure out a way around this issue.

We'd need an exhaustive list of the affected SoCs, and work out if we
can limit the hack to the SMMU driver (cc'ing Robin, who's the one
who'd know about it).



Jazz is not dead, it just smell funny.