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Date:   Mon, 18 Oct 2021 09:50:41 -0600
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Suzuki K Poulose <suzuki.poulose@arm.com>
Cc:     will@kernel.org, catalin.marinas@arm.com,
        anshuman.khandual@arm.com, mike.leach@linaro.org,
        leo.yan@linaro.org, maz@kernel.org, coresight@lists.linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v5 04/15] arm64: errata: Add detection for TRBE write to
 out-of-range
Message-ID: <20211018155041.GA3163131@p14s>
References: <20211014223125.2605031-1-suzuki.poulose@arm.com>
 <20211014223125.2605031-5-suzuki.poulose@arm.com>
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Good morning,

On Thu, Oct 14, 2021 at 11:31:14PM +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

Checkpatch gives me a warning about this line...

> 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

I'm pretty sure this line will also be flagged.

> address faults within the driver.
> 
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  Documentation/arm64/silicon-errata.rst |  4 +++
>  arch/arm64/Kconfig                     | 41 ++++++++++++++++++++++++++
>  arch/arm64/kernel/cpu_errata.c         | 20 +++++++++++++
>  arch/arm64/tools/cpucaps               |  1 +
>  4 files changed, 66 insertions(+)
> 
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index 569a92411dcd..5342e895fb60 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -96,6 +96,8 @@ stable kernels.
>  +----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Cortex-A710     | #2054223        | ARM64_ERRATUM_2054223       |
>  +----------------+-----------------+-----------------+-----------------------------+
> +| ARM            | Cortex-A710     | #2224489        | ARM64_ERRATUM_2224489       |
> ++----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Neoverse-N1     | #1188873,1418040| ARM64_ERRATUM_1418040       |
>  +----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Neoverse-N1     | #1349291        | N/A                         |
> @@ -106,6 +108,8 @@ stable kernels.
>  +----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Neoverse-N2     | #2067961        | ARM64_ERRATUM_2067961       |
>  +----------------+-----------------+-----------------+-----------------------------+
> +| ARM            | Neoverse-N2     | #2253138        | ARM64_ERRATUM_2253138       |
> ++----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | MMU-500         | #841119,826419  | N/A                         |
>  +----------------+-----------------+-----------------+-----------------------------+
>  +----------------+-----------------+-----------------+-----------------------------+
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 39b78460b9d0..f30029f4a9f9 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -740,6 +740,47 @@ config ARM64_ERRATUM_2067961
>  
>  	  If unsure, say Y.
>  
> +config ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +	bool
> +
> +config ARM64_ERRATUM_2253138
> +	bool "Neoverse-N2: 2253138: workaround TRBE writing to address out-of-range"
> +	depends on COMPILE_TEST # Until the CoreSight TRBE driver changes are in
> +	depends on CORESIGHT_TRBE
> +	default y
> +	select ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +	help
> +	  This option adds the workaround for ARM Neoverse-N2 erratum 2253138.
> +
> +	  Affected Neoverse-N2 cores might write to an out-of-range address, not reserved
> +	  for TRBE. Under some conditions, the TRBE might generate a write to the next
> +	  virtually addressed page following the last page of the TRBE address space
> +	  (i.e., the TRBLIMITR_EL1.LIMIT), instead of wrapping around to the base.
> +
> +	  Work around this in the driver by always making sure that there is a
> +	  page beyond the TRBLIMITR_EL1.LIMIT, within the space allowed for the TRBE.
> +
> +	  If unsure, say Y.
> +
> +config ARM64_ERRATUM_2224489
> +	bool "Cortex-A710: 2224489: workaround TRBE writing to address out-of-range"
> +	depends on COMPILE_TEST # Until the CoreSight TRBE driver changes are in
> +	depends on CORESIGHT_TRBE
> +	default y
> +	select ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +	help
> +	  This option adds the workaround for ARM Cortex-A710 erratum 2224489.
> +
> +	  Affected Cortex-A710 cores might write to an out-of-range address, not reserved
> +	  for TRBE. Under some conditions, the TRBE might generate a write to the next
> +	  virtually addressed page following the last page of the TRBE address space
> +	  (i.e., the TRBLIMITR_EL1.LIMIT), instead of wrapping around to the base.
> +
> +	  Work around this in the driver by always making sure that there is a
> +	  page beyond the TRBLIMITR_EL1.LIMIT, within the space allowed for the TRBE.
> +
> +	  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 bdbeac75ead6..e2978b89d4b8 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -364,6 +364,18 @@ static const struct midr_range tsb_flush_fail_cpus[] = {
>  };
>  #endif	/* CONFIG_ARM64_WORKAROUND_TSB_FLUSH_FAILURE */
>  
> +#ifdef CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +static struct midr_range trbe_write_out_of_range_cpus[] = {
> +#ifdef CONFIG_ARM64_ERRATUM_2253138
> +	MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2),
> +#endif
> +#ifdef CONFIG_ARM64_ERRATUM_2224489
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A710),
> +#endif
> +	{},
> +};
> +#endif /* CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE */
> +
>  const struct arm64_cpu_capabilities arm64_errata[] = {
>  #ifdef CONFIG_ARM64_WORKAROUND_CLEAN_CACHE
>  	{
> @@ -577,6 +589,14 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>  		.capability = ARM64_WORKAROUND_TSB_FLUSH_FAILURE,
>  		ERRATA_MIDR_RANGE_LIST(tsb_flush_fail_cpus),
>  	},
> +#endif
> +#ifdef CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +	{
> +		.desc = "ARM erratum 2253138 or 2224489",
> +		.capability = ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE,
> +		.type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
> +		CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
> +	},
>  #endif
>  	{
>  	}
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 2102e15af43d..90628638e0f9 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -55,6 +55,7 @@ WORKAROUND_1508412
>  WORKAROUND_1542419
>  WORKAROUND_TRBE_OVERWRITE_FILL_MODE
>  WORKAROUND_TSB_FLUSH_FAILURE
> +WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
>  WORKAROUND_CAVIUM_23154
>  WORKAROUND_CAVIUM_27456
>  WORKAROUND_CAVIUM_30115
> -- 
> 2.25.4
>