Re: [PATCH v2 02/10] coresight: etm4x: Use Trace Filtering controls dynamically

From: Anshuman Khandual
Date: Thu Jul 29 2021 - 23:50:54 EST

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On 7/23/21 6:16 PM, Suzuki K Poulose wrote:
> The Trace Filtering support (FEAT_TRF) ensures that the ETM
> can be prohibited from generating any trace for a given EL.
> This is much stricter knob, than the TRCVICTLR exception level

Could you please explain 'stricter' ? Are you suggesting that TRCVICTLR
based exception filtering some times might not implement the filtering
even if configured ?

> masks. At the moment, we do a onetime enable trace at user and
> kernel and leave it untouched for the kernel life time.
>
> This patch makes the switch dynamic, by honoring the filters
> set by the user and enforcing them in the TRFCR controls.

TRFCR actually helps in making the exception level filtering dynamic
which was not possible earlier with TRCVICTLR.

> We also rename the cpu_enable_tracing() appropriately to
> cpu_detect_trace_filtering() and the drvdata member
> trfc => trfcr to indicate the "value" of the TRFCR_EL1.

Makes sense.

>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Al Grant <al.grant@xxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> .../coresight/coresight-etm4x-core.c | 61 ++++++++++++++-----
> drivers/hwtracing/coresight/coresight-etm4x.h | 5 +-
> .../coresight/coresight-self-hosted-trace.h | 7 +++
> 3 files changed, 55 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 3e548dac9b05..adba84b29455 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -237,6 +237,43 @@ struct etm4_enable_arg {
> int rc;
> };
>
> +/*
> + * etm4x_prohibit_trace - Prohibit the CPU from tracing at all ELs.
> + * When the CPU supports FEAT_TRF, we could move the ETM to a trace
> + * prohibited state by filtering the Exception levels via TRFCR_EL1.
> + */
> +static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
> +{
> + if (drvdata->trfcr)
> + cpu_prohibit_trace();

Should it be as etm4x_allow_trace() instead, where drvdata->trfcr
indicates the presence of FEAT_TRF - just to be clear ?

/* If the CPU doesn't support FEAT_TRF, nothing to do */
if (!drvdata->trfcr)
return;

cpu_prohibit_trace();

> +}
> +
> +/*
> + * etm4x_allow_trace - Allow CPU tracing in the respective ELs,
> + * as configured by the drvdata->config.mode for the current
> + * session. Even though we have TRCVICTLR bits to filter the
> + * trace in the ELs, it doesn't prevent the ETM from generating
> + * a packet (e.g, TraceInfo) that might contain the addresses from
> + * the excluded levels. Thus we use the additional controls provided
> + * via the Trace Filtering controls (FEAT_TRF) to make sure no trace
> + * is generated for the excluded ELs.
> + */
> +static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
> +{
> + u64 trfcr = drvdata->trfcr;
> +
> + /* If the CPU doesn't support FEAT_TRF, nothing to do */
> + if (!trfcr)
> + return;
> +
> + if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
> + trfcr &= ~TRFCR_ELx_ExTRE;
> + if (drvdata->config.mode & ETM_MODE_EXCL_USER)
> + trfcr &= ~TRFCR_ELx_E0TRE;
> +
> + write_trfcr(trfcr);
> +}
> +
> #ifdef CONFIG_ETM4X_IMPDEF_FEATURE
>
> #define HISI_HIP08_AMBA_ID 0x000b6d01
> @@ -441,6 +478,7 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> if (etm4x_is_ete(drvdata))
> etm4x_relaxed_write32(csa, TRCRSR_TA, TRCRSR);
>
> + etm4x_allow_trace(drvdata);
> /* Enable the trace unit */
> etm4x_relaxed_write32(csa, 1, TRCPRGCTLR);
>
> @@ -719,7 +757,6 @@ static int etm4_enable(struct coresight_device *csdev,
> static void etm4_disable_hw(void *info)
> {
> u32 control;
> - u64 trfcr;
> struct etmv4_drvdata *drvdata = info;
> struct etmv4_config *config = &drvdata->config;
> struct coresight_device *csdev = drvdata->csdev;
> @@ -746,12 +783,7 @@ static void etm4_disable_hw(void *info)
> * If the CPU supports v8.4 Trace filter Control,
> * set the ETM to trace prohibited region.
> */
> - if (drvdata->trfc) {
> - trfcr = read_sysreg_s(SYS_TRFCR_EL1);
> - write_sysreg_s(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE),
> - SYS_TRFCR_EL1);
> - isb();
> - }
> + etm4x_prohibit_trace(drvdata);
> /*
> * Make sure everything completes before disabling, as recommended
> * by section 7.3.77 ("TRCVICTLR, ViewInst Main Control Register,
> @@ -767,9 +799,6 @@ static void etm4_disable_hw(void *info)
> if (coresight_timeout(csa, TRCSTATR, TRCSTATR_PMSTABLE_BIT, 1))
> dev_err(etm_dev,
> "timeout while waiting for PM stable Trace Status\n");
> - if (drvdata->trfc)
> - write_sysreg_s(trfcr, SYS_TRFCR_EL1);
> -
> /* read the status of the single shot comparators */
> for (i = 0; i < drvdata->nr_ss_cmp; i++) {
> config->ss_status[i] =
> @@ -964,15 +993,15 @@ static bool etm4_init_csdev_access(struct etmv4_drvdata *drvdata,
> return false;
> }
>
> -static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
> +static void cpu_detect_trace_filtering(struct etmv4_drvdata *drvdata)
> {
> u64 dfr0 = read_sysreg(id_aa64dfr0_el1);
> u64 trfcr;
>
> + drvdata->trfcr = 0;
> if (!cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRACE_FILT_SHIFT))
> return;
>
> - drvdata->trfc = true;
> /*
> * If the CPU supports v8.4 SelfHosted Tracing, enable
> * tracing at the kernel EL and EL0, forcing to use the
> @@ -986,7 +1015,7 @@ static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
> if (is_kernel_in_hyp_mode())
> trfcr |= TRFCR_EL2_CX;
>
> - write_trfcr(trfcr);
> + drvdata->trfcr = trfcr;
> }
>
> static void etm4_init_arch_data(void *info)
> @@ -1177,7 +1206,7 @@ static void etm4_init_arch_data(void *info)
> /* NUMCNTR, bits[30:28] number of counters available for tracing */
> drvdata->nr_cntr = BMVAL(etmidr5, 28, 30);
> etm4_cs_lock(drvdata, csa);
> - cpu_enable_tracing(drvdata);
> + cpu_detect_trace_filtering(drvdata);
> }
>
> static inline u32 etm4_get_victlr_access_type(struct etmv4_config *config)
> @@ -1673,7 +1702,7 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> int ret = 0;
>
> /* Save the TRFCR irrespective of whether the ETM is ON */
> - if (drvdata->trfc)
> + if (drvdata->trfcr)
> drvdata->save_trfcr = read_trfcr();
> /*
> * Save and restore the ETM Trace registers only if
> @@ -1782,7 +1811,7 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>
> static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> {
> - if (drvdata->trfc)
> + if (drvdata->trfcr)
> write_trfcr(drvdata->save_trfcr);
> if (drvdata->state_needs_restore)
> __etm4_cpu_restore(drvdata);
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 82cba16b73a6..724819592c2e 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -919,7 +919,8 @@ struct etmv4_save_state {
> * @nooverflow: Indicate if overflow prevention is supported.
> * @atbtrig: If the implementation can support ATB triggers
> * @lpoverride: If the implementation can support low-power state over.
> - * @trfc: If the implementation supports Arm v8.4 trace filter controls.
> + * @trfcr: If the CPU supportfs FEAT_TRF, value of the TRFCR_ELx with

Typo here. ^^^^^^ s/supportfs/supports

> + * trace allowed at user and kernel ELs. Otherwise, 0.

The sentence here does not make sense. Is not the exception level ELx and EL0
can be filtered out independently ? Should this be something like ...

"If the CPU supports FEAT_TRF, value of the TRFCR_ELx - indicating whether
trace is allowed at user [and/or] kernel ELs. Otherwise, 0."

> * @config: structure holding configuration parameters.
> * @save_trfcr: Saved TRFCR_EL1 register during a CPU PM event.
> * @save_state: State to be preserved across power loss
> @@ -972,7 +973,7 @@ struct etmv4_drvdata {
> bool nooverflow;
> bool atbtrig;
> bool lpoverride;
> - bool trfc;
> + u64 trfcr;
> struct etmv4_config config;
> u64 save_trfcr;
> struct etmv4_save_state *save_state;
> diff --git a/drivers/hwtracing/coresight/coresight-self-hosted-trace.h b/drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> index 53b35a28075e..586d26e0cba3 100644
> --- a/drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> +++ b/drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> @@ -22,4 +22,11 @@ static inline void write_trfcr(u64 val)
> isb();
> }
>
> +static inline void cpu_prohibit_trace(void)
> +{
> + u64 trfcr = read_trfcr();
> +
> + /* Prohibit tracing at EL0 & the kernel EL */
> + write_trfcr(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE));
> +}
> #endif /* __CORESIGHT_SELF_HOSTED_TRACE_H */
>

Next message: Akhil P Oommen: "Re: [PATCH] drm: msm: Add 680 gpu to the adreno gpu list"
Previous message: Doug Smythies: "Re: [PATCH v1 0/5] cpuidle: teo: Rework the idle state selection logic"
Next in thread: Suzuki K Poulose: "Re: [PATCH v2 02/10] coresight: etm4x: Use Trace Filtering controls dynamically"
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