linux-kernel - Re: [PATCH 10/10] arm64: errata: Add workaround for TSB flush failures

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Message-ID: <20210802112712.GE18685@arm.com>
Date:   Mon, 2 Aug 2021 12:27:12 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, anshuman.khandual@....com,
        will@...nel.org, james.morse@....com, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, leo.yan@...aro.org, maz@...nel.org,
        mark.rutland@....com
Subject: Re: [PATCH 10/10] arm64: errata: Add workaround for TSB flush
 failures

On Wed, Jul 28, 2021 at 02:52:17PM +0100, Suzuki K Poulose wrote:
> 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 everytime 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>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>

With Marc's comments addressed:

Acked-by: Catalin Marinas <catalin.marinas@....com>