linux-kernel - [patch 1/2] x86/fpu: Simplify fpregs

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Message-Id: <20201027101349.455380473@linutronix.de>
Date:   Tue, 27 Oct 2020 11:09:50 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [patch 1/2] x86/fpu: Simplify fpregs_[un]lock()

There is no point in disabling preemption and then disabling bottom
halfs.

Just disabling bottom halfs is sufficient as it implicitly disables
preemption on !RT kernels.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/include/asm/fpu/api.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -29,17 +29,18 @@ 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.
  */
 static inline void fpregs_lock(void)
 {
-	preempt_disable();
 	local_bh_disable();
 }
 
 static inline void fpregs_unlock(void)
 {
 	local_bh_enable();
-	preempt_enable();
 }
 
 #ifdef CONFIG_X86_DEBUG_FPU