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

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Date:   Fri, 11 May 2018 17:06:20 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Greg KH <greg@...ah.com>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        will.deacon@....com, mark.rutland@....com
Subject: Re: [PATCH] [stable 4.9] arm64: Add work around for Arm Cortex-A55
 Erratum 1024718

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@...r.kernel.org # v4.9
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>> 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@arm.com
> 
> 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