linux-kernel - [PATCH 2/3] x86/fpu: Make FPU protection reuse common helper

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Message-Id: <20210722175157.1367122-3-valentin.schneider@arm.com>
Date:   Thu, 22 Jul 2021 18:51:56 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rt-users@...r.kernel.org, x86@...nel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Mark Brown <broonie@...nel.org>,
        Dave Martin <Dave.Martin@....com>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH 2/3] x86/fpu: Make FPU protection reuse common helper

The newly-introduced preempt_{enable, disable}_bh() helpers are an exact
stand-in for fpregs_{lock, unlock}(). Use them there.

No change in behaviour intended.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 arch/x86/include/asm/fpu/api.h | 19 ++-----------------
 1 file changed, 2 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 62cf3e4c06fb..ffebb9316bfd 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -54,31 +54,16 @@ static inline void kernel_fpu_begin(void)
  * 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)
 {
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_bh_disable();
-	else
-		preempt_disable();
+	preempt_disable_bh();
 }
 
 static inline void fpregs_unlock(void)
 {
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_bh_enable();
-	else
-		preempt_enable();
+	preempt_enable_bh();
 }
 
 #ifdef CONFIG_X86_DEBUG_FPU
-- 
2.25.1