Re: [PATCH] [stable 4.9] arm64: Add work around for Arm Cortex-A55 Erratum 1024718

[Suzuki K Poulose]

On 11/05/18 16:47, Greg KH wrote:
> On Fri, May 11, 2018 at 02:51:15PM +0100, Suzuki K Poulose wrote:
> > commit ece1397cbc89c51914fae1aec729539cfd8bd62b upstream
> >
> > Some variants of the Arm Cortex-55 cores (r0p0, r0p1, r1p0) suffer
> > from an erratum 1024718, which causes incorrect updates when DBM/AP
> > bits in a page table entry is modified without a break-before-make
> > sequence. The work around is to disable the hardware DBM feature
> > on the affected cores. The hardware Access Flag management features
> > is not affected.
> >
> > The hardware DBM feature is a non-conflicting capability, i.e, the
> > kernel could handle cores using the feature and those without having
> > the features running at the same time. So this work around is detected
> > at early boot time, rather than delaying it until the CPUs are brought
> > up into the kernel with MMU turned on. This also avoids other complexities
> > with late CPUs turning online, with or without the hardware DBM features.
> >
> > Cc: stable@xxxxxxxxxxxxxxx # v4.9
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> > Note: The upstream commit is on top of a reworked capability
> > infrastructure for arm64 heterogeneous systems, which allows
> > delaying the CPU model checks. This backport is based on the
> > original version of the patch [0], which checks the affected
> > CPU models during the early boot.
> >
> > [0] https://lkml.kernel.org/r/20180116102323.3470-1-suzuki.poulose@xxxxxxx
>
> Now applied, thanks.

Greg,

I have the backport for v4.4 ready. But it needs to cherry-pick a commit
(commit 30b5ba5cf33 : arm64: introduce mov_q macro to move a constant into a 64-bit register)
which adds the assembly helper and that seems to result in a conflict with
an obvious resolution. What do you prefer in this case ?

1) Go ahead with the cherry-pick

Or

2) Fold the pre-req patch (which is about 30 lines of changes) in the back port

Cheers
Suzuki