Re: [PATCH v2 14/23] coresight: trbe: Treat access not allowed stops as fatal

[James Clark <james.clark@linaro.org>]

On 16/10/2026 17:55, Leo Yan wrote:
> Arm ARM (ARM DDI 0487 M.b), the rule R_RRCNN in "D6.11 UNPREDICTABLE
> behavior" permits a buffer management event when the effective SCR_EL3
> security state does not match the owning Security state. This can stop
> collection with IRQ=1, S=1, EC=0 and BSC=0 while leaving the other
> status fields unchanged.
> 
> With EA and WRAP clear, trbe_get_fault_act() currently returns SPURIOUS
> for this status. The spurious handler re-enables TRBE without clearing
> S, so collection can remain stopped. A retained WRAP indication can
> instead cause the status to be treated as a normal buffer wrap.
> 
> Recognize this architecturally permitted stopped status as an access
> not allowed error and return FATAL so the fatal handling reports
> truncated trace. Check the syndrome before WRAP and do not exclude
> TRG, since both fields are left unchanged by this stop. Check the saved
> IRQ bit to preserve updates without a pending interrupt.
> 
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-trbe.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 4aeed1a17c4bf1653fb41731ac15f31feec7ed2e..1c585b6123df2f20d08747678d836742ce9564cc 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -708,6 +708,14 @@ static enum trbe_fault_action trbe_get_fault_act(struct perf_output_handle *hand
>   		goto out_fatal;
>   	}
>   
> +	/* An access not allowed stop can leave WRAP and TRG unchanged. */
> +	if (is_trbe_irq(trbsr) && !is_trbe_running(trbsr) &&
> +	    ec == TRBSR_EL1_EC_OTHER &&
> +	    bsc == TRBSR_EL1_BSC_NOT_STOPPED) {
> +		err_str = "Trace buffer access not allowed";
> +		goto out_fatal;
> +	}
> +
>   	if (is_trbe_wrap(trbsr))
>   		return TRBE_FAULT_ACT_WRAP;
>   
> 
Reviewed-by: James Clark <james.clark@linaro.org>