linux-kernel - Re: [PATCH 10/19] coresight: trbe: Always check fault action when updating buffer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e22497a2-1019-4eec-95b4-b6fd80090a3f@linaro.org>
Date: Tue, 16 Dec 2025 17:34:20 +0200
From: James Clark <james.clark@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach
 <mike.leach@...aro.org>, Anshuman Khandual <anshuman.khandual@....com>,
 Yeoreum Yun <yeoreum.yun@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Tamas Petz <tamas.petz@....com>,
 Tamas Zsoldos <tamas.zsoldos@....com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 10/19] coresight: trbe: Always check fault action when
 updating buffer



On 01/12/2025 13:22, Leo Yan wrote:
> The current code checks the fault action only via the IRQ status bit,
> which is unreliable due to possible hardware latency.

This makes it sound like it's fixing a bug, but without a fixes: tag I'm 
assuming it's not a bug. Also I don't get how the change improves the 
latency situation, it still calls trbe_get_fault_act() basically in the 
same place. I think there might be another reason like it makes the code 
cleaner for a later change? Or the commit message needs some elaboration.

> 
> Move the fault action check out of the IRQ status condition.  This also
> causes the buffer size to be calculated for non-WRAP and fault cases,
> which is fine since the write pointer is trusted for the calculation.
> 
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>   drivers/hwtracing/coresight/coresight-trbe.c | 17 +++--------------
>   1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index f56ecdeaa6596afb440e4d53732e08a85f9bf89d..e579ea98523c24d23a0cd265dcdd0a46b52b52da 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -806,7 +806,6 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
>   	enum trbe_fault_action act;
>   	unsigned long size, status;
>   	unsigned long flags;
> -	bool wrap = false;
>   
>   	WARN_ON(buf->cpudata != cpudata);
>   	WARN_ON(cpudata->cpu != smp_processor_id());
> @@ -858,21 +857,11 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
>   		 */
>   		clr_trbe_irq();
>   		isb();
> -
> -		act = trbe_get_fault_act(handle, status);
> -		/*
> -		 * If this was not due to a WRAP event, we have some
> -		 * errors and as such buffer is empty.
> -		 */
> -		if (act != TRBE_FAULT_ACT_WRAP) {
> -			size = 0;
> -			goto done;
> -		}
> -
> -		wrap = true;
>   	}
>   
> -	size = trbe_get_trace_size(handle, buf, wrap);
> +	act = trbe_get_fault_act(handle, status);
> +
> +	size = trbe_get_trace_size(handle, buf, act == TRBE_FAULT_ACT_WRAP);
>   
>   done:
>   	local_irq_restore(flags);
>