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Date: Wed, 5 Jan 2022 10:13:06 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
coresight@...ts.linaro.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] coresight: trbe: Work around the invalid prohibited
states
Hi Anshuman
On 05/01/2022 05:05, Anshuman Khandual wrote:
> TRBE implementations affected by Arm erratum #2038923 might get TRBE into
> an inconsistent view on whether trace is prohibited within the CPU. As a
> result, the trace buffer or trace buffer state might be corrupted. This
> happens after TRBE buffer has been enabled by setting TRBLIMITR_EL1.E,
> followed by just a single context synchronization event before execution
> changes from a context, in which trace is prohibited to one where it isn't,
> or vice versa. In these mentioned conditions, the view of whether trace is
> prohibited is inconsistent between parts of the CPU, and the trace buffer
> or the trace buffer state might be corrupted.
>
> Work around this problem in the TRBE driver by preventing an inconsistent
> view of whether the trace is prohibited or not based on TRBLIMITR_EL1.E by
> immediately following a change to TRBLIMITR_EL1.E with at least one ISB
> instruction before an ERET, or two ISB instructions if no ERET is to take
> place. This adds a new cpu errata in arm64 errata framework and also
> updates TRBE driver as required.
>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Suzuki Poulose <suzuki.poulose@....com>
> Cc: coresight@...ts.linaro.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Documentation/arm64/silicon-errata.rst | 2 +
> arch/arm64/Kconfig | 23 ++++++++++
> arch/arm64/kernel/cpu_errata.c | 9 ++++
> arch/arm64/tools/cpucaps | 1 +
> drivers/hwtracing/coresight/coresight-trbe.c | 47 +++++++++++++++-----
> 5 files changed, 72 insertions(+), 10 deletions(-)
As with the previous patch, it may be a good idea to split the
patch to arm64 and trbe parts.
>
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index c9b30e6c2b6c..e0ef3e9a4b8b 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -54,6 +54,8 @@ stable kernels.
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A510 | #2064142 | ARM64_ERRATUM_2064142 |
> +----------------+-----------------+-----------------+-----------------------------+
> +| ARM | Cortex-A510 | #2038923 | ARM64_ERRATUM_2038923 |
> ++----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A53 | #826319 | ARM64_ERRATUM_826319 |
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A53 | #827319 | ARM64_ERRATUM_827319 |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 2105b68d88db..026e34fb6fad 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -796,6 +796,29 @@ config ARM64_ERRATUM_2064142
>
> If unsure, say Y.
>
> +config ARM64_ERRATUM_2038923
> + bool "Cortex-A510: 2038923: workaround TRBE corruption with enable"
> + depends on CORESIGHT_TRBE
> + default y
> + help
> + This option adds the workaround for ARM Cortex-A510 erratum 2038923.
> +
> + Affected Cortex-A510 core might cause an inconsistent view on whether trace is
> + prohibited within the CPU. As a result, the trace buffer or trace buffer state
> + might be corrupted. This happens after TRBE buffer has been enabled by setting
> + TRBLIMITR_EL1.E, followed by just a single context synchronization event before
> + execution changes from a context, in which trace is prohibited to one where it
> + isn't, or vice versa. In these mentioned conditions, the view of whether trace
> + is prohibited is inconsistent between parts of the CPU, and the trace buffer or
> + the trace buffer state might be corrupted.
> +
> + Work around this in the driver by preventing an inconsistent view of whether the
> + trace is prohibited or not based on TRBLIMITR_EL1.E by immediately following a
> + change to TRBLIMITR_EL1.E with at least one ISB instruction before an ERET, or
> + two ISB instructions if no ERET is to take place.
> +
> + If unsure, say Y.
> +
> config CAVIUM_ERRATUM_22375
> bool "Cavium erratum 22375, 24313"
> default y
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index cbb7d5a9aee7..60b0c1f1d912 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -607,6 +607,15 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
> ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2)
> },
> #endif
> +#ifdef CONFIG_ARM64_ERRATUM_2038923
> + {
> + .desc = "ARM erratum 2038923",
> + .capability = ARM64_WORKAROUND_2038923,
> +
> + /* Cortex-A510 r0p0 - r0p2 */
> + ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2)
> + },
> +#endif
> {
> }
> };
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index fca3cb329e1d..45a06d36d080 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -56,6 +56,7 @@ WORKAROUND_1463225
> WORKAROUND_1508412
> WORKAROUND_1542419
> WORKAROUND_2064142
> +WORKAROUND_2038923
> WORKAROUND_TRBE_OVERWRITE_FILL_MODE
> WORKAROUND_TSB_FLUSH_FAILURE
> WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index ec24b62b2cec..0689c6dab96d 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -92,11 +92,13 @@ struct trbe_buf {
> #define TRBE_WORKAROUND_OVERWRITE_FILL_MODE 0
> #define TRBE_WORKAROUND_WRITE_OUT_OF_RANGE 1
> #define TRBE_WORKAROUND_SYSREG_WRITE_FAILURE 2
> +#define TRBE_WORKAROUND_CORRUPTION_WITH_ENABLE 3
>
> static int trbe_errata_cpucaps[] = {
> [TRBE_WORKAROUND_OVERWRITE_FILL_MODE] = ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE,
> [TRBE_WORKAROUND_WRITE_OUT_OF_RANGE] = ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE,
> [TRBE_WORKAROUND_SYSREG_WRITE_FAILURE] = ARM64_WORKAROUND_2064142,
> + [TRBE_WORKAROUND_CORRUPTION_WITH_ENABLE] = ARM64_WORKAROUND_2038923,
> -1, /* Sentinel, must be the last entry */
> };
>
> @@ -174,6 +176,11 @@ static inline bool trbe_may_fail_sysreg_write(struct trbe_cpudata *cpudata)
> return trbe_has_erratum(cpudata, TRBE_WORKAROUND_SYSREG_WRITE_FAILURE);
> }
>
> +static inline bool trbe_may_corrupt_with_enable(struct trbe_cpudata *cpudata)
> +{
minor nit: trbe_needs_{ctxt_sync, isb}_after_enable() ?
> + return trbe_has_erratum(cpudata, TRBE_WORKAROUND_CORRUPTION_WITH_ENABLE);
> +}
> +
> static int trbe_alloc_node(struct perf_event *event)
> {
> if (event->cpu == -1)
> @@ -187,6 +194,30 @@ static inline void trbe_drain_buffer(void)
> dsb(nsh);
> }
>
> +static inline void set_trbe_enabled(struct trbe_cpudata *cpudata)
> +{
> + u64 trblimitr = read_sysreg_s(SYS_TRBLIMITR_EL1);
minor nit: This implies we do the TRBE programming in the following
manner in the common case (i.e, TRBE enabled in the beginning of a
session).
-> set TRBE LIMIT
-> read TRBE LIMIT
-> set TRBE ENABLED
Could we please optimize this ? I believe the buf->trbe_limit
must hold the LIMITR value at any point in time. And thus this
function could simply be :
set_trbe_enabled(trbe_buf)
{
limitr = trbe_buf->limit | LIMITR_ENABLE
write(limitr, TRBLIMITR_EL1);
...
}
Otherwise looks good to me
Suzuki
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