diff options
| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2022-05-05 18:32:06 +0200 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2022-05-16 19:15:46 +0100 |
| commit | 696207d4258b2ab66dbd1655a7cfb3e978889085 (patch) | |
| tree | 26fdce18b68129c68f624ee622f0f78b60216faf /arch/arm64 | |
| parent | a1259dd807192917eb98603f8bc7b43f70cea5b9 (diff) | |
arm64/sve: Make kernel FPU protection RT friendly
Non RT kernels need to protect FPU against preemption and bottom half
processing. This is achieved by disabling bottom halves via
local_bh_disable() which implictly disables preemption.
On RT kernels this protection mechanism is not sufficient because
local_bh_disable() does not disable preemption. It serializes bottom half
related processing via a CPU local lock.
As bottom halves are running always in thread context on RT kernels
disabling preemption is the proper choice as it implicitly prevents bottom
half processing.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220505163207.85751-3-bigeasy@linutronix.de
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64')
| -rw-r--r-- | arch/arm64/kernel/fpsimd.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 6e53badff8a6..a568735b7c2e 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -237,10 +237,19 @@ static void __get_cpu_fpsimd_context(void) * * The double-underscore version must only be called if you know the task * can't be preempted. + * + * On RT kernels local_bh_disable() is not sufficient because it only + * serializes soft interrupt related sections via a local lock, but stays + * preemptible. Disabling preemption is the right choice here as bottom + * half processing is always in thread context on RT kernels so it + * implicitly prevents bottom half processing as well. */ static void get_cpu_fpsimd_context(void) { - local_bh_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_disable(); + else + preempt_disable(); __get_cpu_fpsimd_context(); } @@ -261,7 +270,10 @@ static void __put_cpu_fpsimd_context(void) static void put_cpu_fpsimd_context(void) { __put_cpu_fpsimd_context(); - local_bh_enable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_enable(); + else + preempt_enable(); } static bool have_cpu_fpsimd_context(void) |