diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2020-10-27 13:09:51 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-11-11 16:35:16 +0300 |
| commit | cba08c5dc6dc1a906a0b5ddac9a9ac6c9a64f2e8 (patch) | |
| tree | 7ce4592cb4d33bfdf4d19169be49bddbf153c9d2 /arch/x86/include/asm/fpu/api.h | |
| parent | 5f0c71278d6848b4809f83af90f28196e1505ab1 (diff) | |
| download | linux-cba08c5dc6dc1a906a0b5ddac9a9ac6c9a64f2e8.tar.xz | |
x86/fpu: 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 halfs 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 halfs 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: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201027101349.588965083@linutronix.de
Diffstat (limited to 'arch/x86/include/asm/fpu/api.h')
| -rw-r--r-- | arch/x86/include/asm/fpu/api.h | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index 2c5bef78a484..a5aba4ab0224 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -32,15 +32,29 @@ extern void fpregs_mark_activate(void); * * local_bh_disable() protects against both preemption and soft interrupts * on !RT kernels. + * + * 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. + * + * Disabling preemption also serializes against kernel_fpu_begin(). */ static inline void fpregs_lock(void) { - local_bh_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_disable(); + else + preempt_disable(); } static inline void fpregs_unlock(void) { - local_bh_enable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_enable(); + else + preempt_enable(); } #ifdef CONFIG_X86_DEBUG_FPU |