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Date: Mon, 14 Dec 2020 20:22:21 -0000 From: Thomas Gleixner <tglx@...utronix.de> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, x86@...nel.org Subject: [GIT pull] x86/fpu for v5.11-rc1 Linus, please pull the latest x86/fpu branch from: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-fpu-2020-12-14 up to: cba08c5dc6dc: x86/fpu: Make kernel FPU protection RT friendly X86 FPU updates: - Simplify the FPU protection for !RT kernels - Add the RT variant of FPU protections Thanks, tglx ------------------> Thomas Gleixner (2): x86/fpu: Simplify fpregs_[un]lock() x86/fpu: Make kernel FPU protection RT friendly arch/x86/include/asm/fpu/api.h | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index dcd9503b1098..a5aba4ab0224 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -29,17 +29,32 @@ extern void fpregs_mark_activate(void); * A context switch will (and softirq might) save CPU's FPU registers to * fpu->state and set TIF_NEED_FPU_LOAD leaving CPU's FPU registers in * a random state. + * + * 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) { - preempt_disable(); - local_bh_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_disable(); + else + preempt_disable(); } static inline void fpregs_unlock(void) { - local_bh_enable(); - preempt_enable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + local_bh_enable(); + else + preempt_enable(); } #ifdef CONFIG_X86_DEBUG_FPU
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