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Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0155-x86-fpu-Make-kernel-FPU-protection-RT-friendly.patch | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/debian/patches-rt/0155-x86-fpu-Make-kernel-FPU-protection-RT-friendly.patch b/debian/patches-rt/0155-x86-fpu-Make-kernel-FPU-protection-RT-friendly.patch new file mode 100644 index 000000000..f28c1aace --- /dev/null +++ b/debian/patches-rt/0155-x86-fpu-Make-kernel-FPU-protection-RT-friendly.patch @@ -0,0 +1,64 @@ +From f6a993a6144299a8693fa151d042c3997238cd54 Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Tue, 27 Oct 2020 11:09:51 +0100 +Subject: [PATCH 155/323] x86/fpu: Make kernel FPU protection RT friendly +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +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 +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + arch/x86/include/asm/fpu/api.h | 18 ++++++++++++++++-- + 1 file changed, 16 insertions(+), 2 deletions(-) + +diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h +index 5174c0a640ef..ad2fee785310 100644 +--- a/arch/x86/include/asm/fpu/api.h ++++ b/arch/x86/include/asm/fpu/api.h +@@ -43,15 +43,29 @@ static inline void kernel_fpu_begin(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 +-- +2.43.0 + |