linux-kernel - Re: [PATCH v2 15/17] arm64: Add erratum detection for TRBE write to out-of-range

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Message-ID: <YV8cCBS1XWKLv+4G@arm.com>
Date:   Thu, 7 Oct 2021 17:10:48 +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,
        maz@...nel.org, mark.rutland@....com, james.morse@....com,
        anshuman.khandual@....com, leo.yan@...aro.org,
        mike.leach@...aro.org, mathieu.poirier@...aro.org, will@...nel.org,
        lcherian@...vell.com, coresight@...ts.linaro.org
Subject: Re: [PATCH v2 15/17] arm64: Add erratum detection for TRBE write to
 out-of-range

On Tue, Sep 21, 2021 at 02:41:19PM +0100, Suzuki K Poulose wrote:
> Arm Neoverse-N2 and Cortex-A710 cores are affected by an erratum where the
> trbe, under some circumstances, might write upto 64bytes to an address after
> the Limit as programmed by the TRBLIMITR_EL1.LIMIT. This might -
> 
>   - Corrupt a page in the ring buffer, which may corrupt trace from a
>     previous session, consumed by userspace.
>   - Hit the guard page at the end of the vmalloc area and raise a fault.
> 
> To keep the handling simpler, we always leave the last page from the
> range, which TRBE is allowed to write. This can be achieved by ensuring
> that we always have more than a PAGE worth space in the range, while
> calculating the LIMIT for TRBE. And then the LIMIT pointer can be adjusted
> to leave the PAGE (TRBLIMITR.LIMIT -= PAGE_SIZE), out of the TRBE range
> while enabling it. This makes sure that the TRBE will only write to an area
> within its allowed limit (i.e, [head-head+size]) and we do not have to handle
> address faults within the driver.
> 
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>

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