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

[Robin Murphy]

On 11/02/2019 14:59, 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.

And even if we *were* to just try papering over the observed extent of 
the issue, I'd still be inclined to confine it to arm-smmu.c where the 
impact is finite and minimal - of the 4 instances of writel(0) there, 3 
of them don't care what the data is (so could just reuse the base 
register or similar) and the other one already has a zero in a GPR to 
hand by construction.

Robin.