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SubjectRe: [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: # v4.9
>> Cc: Catalin Marinas <>
>> Cc: Mark Rutland <>
>> Cc: Will Deacon <>
>> Signed-off-by: Suzuki K Poulose <>
>> ---
>> 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]
> Now applied, thanks.


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


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


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