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

[Catalin Marinas]

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@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

With Marc's comments addressed:

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