[PATCH v3 4/6] arm: Add icache invalidation on switch_mm for Cortex-A15

[Florian Fainelli]

On 01/25/2018 07:21 AM, Marc Zyngier wrote:
> In order to avoid aliasing attacks against the branch predictor,
> Cortex-A15 require to invalidate the BTB when switching
> from one user context to another. The only way to do so on this
> CPU is to perform an ICIALLU, having set ACTLR[0] to 1 from secure
> mode.

Even though this is a platform design mistake, let's say your Linux
kernel boots in secure supervisor mode, we could have code
that tries to set ACTLR[0] as early as possible, since the writes are
ignored if executing from non-secure mode. If Linux is booted normally
either PL1 or PL2 non-secure we could still check ACTLR[0].

My concern is that without doing this, we may have a hard time catching
improper firmware as well as having bogus bug reports. This is
completely RFC though since:

- I could not quite figure out yet why update ca15_actlr_status from
assembly is not reflected in the C code despite using PC relative loads

- this is done in __ca15mp_setup and __b15mp_setup because we know by
then that we have either of these two CPUs but we could presumably move
this check under a Kconfig option and earlier where all erratas are checked

-- 
Florian

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