linux-kernel - Re: [PATCH 5.15 2/4] arm64: errata: Add workaround for TSB flush failures

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Message-ID: <2023072131-supremacy-modify-f9ff@gregkh>
Date:   Fri, 21 Jul 2023 07:27:29 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Easwar Hariharan <eahariha@...ux.microsoft.com>
Cc:     stable@...r.kernel.org, easwar.hariharan@...rosoft.com,
        catalin.marinas@....com, will@...nel.org, corbet@....net,
        robin.murphy@....com, joro@...tes.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [PATCH 5.15 2/4] arm64: errata: Add workaround for TSB flush
 failures

On Thu, Jul 20, 2023 at 04:23:32PM -0700, Easwar Hariharan wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> commit fa82d0b4b833790ac4572377fb777dcea24a9d69 upstream
> 
> Arm Neoverse-N2 (#2067961) and Cortex-A710 (#2054223) suffers
> from errata, where a TSB (trace synchronization barrier)
> fails to flush the trace data completely, when executed from
> a trace prohibited region. In Linux we always execute it
> after we have moved the PE to trace prohibited region. So,
> we can apply the workaround every time a TSB is executed.
> 
> The work around is to issue two TSB consecutively.
> 
> NOTE: This errata is defined as LOCAL_CPU_ERRATUM, implying
> that a late CPU could be blocked from booting if it is the
> first CPU that requires the workaround. This is because we
> do not allow setting a cpu_hwcaps after the SMP boot. The
> other alternative is to use "this_cpu_has_cap()" instead
> of the faster system wide check, which may be a bit of an
> overhead, given we may have to do this in nvhe KVM host
> before a guest entry.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Link: https://lore.kernel.org/r/20211019163153.3692640-4-suzuki.poulose@arm.com
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  Documentation/arm64/silicon-errata.rst |  4 ++++
>  arch/arm64/Kconfig                     | 33 ++++++++++++++++++++++++++
>  arch/arm64/include/asm/barrier.h       | 16 ++++++++++++-
>  arch/arm64/kernel/cpu_errata.c         | 19 +++++++++++++++
>  arch/arm64/tools/cpucaps               |  1 +
>  5 files changed, 72 insertions(+), 1 deletion(-)

As you forwarded this patch on to me, you forgot to sign-off on it :(

I've taken patch 1/4 of this series, but not the rest.  Please redo
them, and send the needed backports for 6.1.y and 6.4.y as a separate
series (obviously I can't apply patches in a series to trees that
already have them.)

thanks,

greg k-h