[PATCH 5.9 063/252] arm64: errata: Fix handling of 1418040 with late CPU onlining

Greg Kroah-Hartman
2020-11-23T12:45:03Z

From: Will Deacon <will@kernel.org>

[ Upstream commit f969f03888b9438fdb227b6460d99ede5737326d ]

In a surprising turn of events, it transpires that CPU capabilities
configured as ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE are never set as the
result of late-onlining. Therefore our handling of erratum 1418040 does
not get activated if it is not required by any of the boot CPUs, even
though we allow late-onlining of an affected CPU.

In order to get things working again, replace the cpus_have_const_cap()
invocation with an explicit check for the current CPU using
this_cpu_has_cap().

Cc: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201106114952.10032-1-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/cpufeature.h | 2 ++
arch/arm64/kernel/process.c | 5 ++---
2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 89b4f0142c287..a986ecd0b0074 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -268,6 +268,8 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
/*
* CPU feature detected at boot time based on feature of one or more CPUs.
* All possible conflicts for a late CPU are ignored.
+ * NOTE: this means that a late CPU with the feature will *not* cause the
+ * capability to be advertised by cpus_have_*cap()!
*/
#define ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE \
(ARM64_CPUCAP_SCOPE_LOCAL_CPU | \
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f1804496b9350..2da5f3f9d345f 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -526,14 +526,13 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
bool prev32, next32;
u64 val;

- if (!(IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) &&
- cpus_have_const_cap(ARM64_WORKAROUND_1418040)))
+ if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040))
return;

prev32 = is_compat_thread(task_thread_info(prev));
next32 = is_compat_thread(task_thread_info(next));

- if (prev32 == next32)
+ if (prev32 == next32 || !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
return;

val = read_sysreg(cntkctl_el1);
--
2.27.0