5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Beata Michalska [ Upstream commit 45f7304679875eb000d67e194090ee7abd05c89c ] Cortex-A725 erratum 3821522 affects the CNT_CYCLES event, which can incur a significant increment error when a CPU enters and subsequently exits WFE or WFI, and may no longer track the system counter frequency. The AMEVCNTR01_EL0 counter is used as the AMU constant counter for frequency invariance and CPPC FFH feedback counters. Wire the affected Cortex-A725 range into the shared broken AMU constant-counter capability so the affected counter is treated as unavailable by returning zero in the AMU counter paths. This prevents the broken counter from being used as a reference source. The erratum can also affect PMUv3 users of the CNT_CYCLES event, but this workaround intentionally does not change PMU event handling. Hiding or rejecting the PMU event from the erratum code would change the perf-visible PMU event interface, including raw event selection, and would need a separate PMU-specific approach rather than being folded into the AMU reference-counter workaround. Cc: stable@vger.kernel.org Signed-off-by: Beata Michalska Reviewed-by: Vladimir Murzin Signed-off-by: Will Deacon [ Beata: Drop the changes to CPPC/FFH support as those are not available here. ] Signed-off-by: Beata Michalska Signed-off-by: Sasha Levin --- Documentation/arm64/silicon-errata.rst | 2 ++ arch/arm64/Kconfig | 22 ++++++++++++++++++++++ arch/arm64/kernel/cpu_errata.c | 4 ++++ 3 files changed, 28 insertions(+) diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst index 98d794cc16d73..01676230ee174 100644 --- a/Documentation/arm64/silicon-errata.rst +++ b/Documentation/arm64/silicon-errata.rst @@ -128,6 +128,8 @@ stable kernels. +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-A725 | #3456106 | ARM64_ERRATUM_3194386 | +----------------+-----------------+-----------------+-----------------------------+ +| ARM | Cortex-A725 | #3821522 | ARM64_ERRATUM_3821522 | ++----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #3324344 | ARM64_ERRATUM_3194386 | +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #4193791 | ARM64_ERRATUM_4118414 | diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index ae4036d549fc9..086d2cd505264 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -699,6 +699,28 @@ config ARM64_ERRATUM_2457168 If unsure, say Y. +config ARM64_ERRATUM_3821522 + bool "Cortex-A725: 3821522: workaround for possible CNT_CYCLES increment error due to WFE/WFI" + depends on ARM64_AMU_EXTN + select ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT + default y + help + This option adds the workaround for ARM Cortex-A725 erratum 3821522. + + On affected A725 cores, the CNT_CYCLES event may incur a significant + increment error when entering and subsequently exiting WFx. + As a result, the CNT_CYCLES may diverge from the system counter + frequency at which it is expected to increment. + This renders the AMU counter AMEVCNTR01, that implements CNT_CYCLES, + being unreliable and unsuitable for use. + + Since there is no hardware workaround, reads of the affected CNT_CYCLES + counter return 0 in the relevant paths. This causes users of the counter + to treat it as unavailable and is functionally equivalent to firmware + disabling the affected counter. + + If unsure, say Y. + config ARM64_ERRATUM_3194386 bool "Cortex-*/Neoverse-*: workaround for MSR SSBS not self-synchronizing" default y diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index df83ff9a767d0..77ad3421d6923 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -265,6 +265,10 @@ static const struct midr_range workaround_amu_constcnt_list[] = { #ifdef CONFIG_ARM64_ERRATUM_2457168 /* Cortex-A510 r0p0-r1p1 */ MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1), +#endif +#ifdef CONFIG_ARM64_ERRATUM_3821522 + /* Cortex-A725 r0p0 - r0p2 */ + MIDR_RANGE(MIDR_CORTEX_A725, 0, 0, 0, 2), #endif {} }; -- 2.53.0