linux-kernel - Re: [PATCH 2/2] [stable 4.4] arm64: Add work around for Arm Cortex-A55 Erratum 1024718

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Date:   Thu, 17 May 2018 11:01:15 +0200
From:   Greg KH <greg@...ah.com>
To:     Suzuki K Poulose <suzuki.poulose@....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, dave.martin@....com
Subject: Re: [PATCH 2/2] [stable 4.4] arm64: Add work around for Arm
 Cortex-A55 Erratum 1024718

On Mon, May 14, 2018 at 12:01:04PM +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 # v4.4
> 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

Thanks for these, now queued up.

greg k-h