linux-kernel - [PATCH v3 1/2] x86/fpu: Replace in_kernel_fpu with kernel_fpu

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Message-ID: <20250520152938.21881-2-ebiggers@kernel.org>
Date: Tue, 20 May 2025 08:29:37 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org,
	linux-pm@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ayush Jain <Ayush.Jain3@....com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH v3 1/2] x86/fpu: Replace in_kernel_fpu with kernel_fpu_allowed

From: Eric Biggers <ebiggers@...gle.com>

Replace the per-CPU bool in_kernel_fpu with kernel_fpu_allowed which
carries the opposite meaning.  Initialize to true instead of false.  No
functional change.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 arch/x86/kernel/fpu/core.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 948b4f5fad99c..6495259a23962 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -43,11 +43,11 @@ struct fpu_state_config fpu_user_cfg __ro_after_init;
  * depending on the FPU hardware format:
  */
 struct fpstate init_fpstate __ro_after_init;
 
 /* Track in-kernel FPU usage */
-static DEFINE_PER_CPU(bool, in_kernel_fpu);
+static DEFINE_PER_CPU(bool, kernel_fpu_allowed) = true;
 
 /*
  * Track which context is using the FPU on the CPU:
  */
 DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
@@ -75,11 +75,11 @@ bool irq_fpu_usable(void)
 	 * In kernel FPU usage already active?  This detects any explicitly
 	 * nested usage in task or softirq context, which is unsupported.  It
 	 * also detects attempted usage in a hardirq that has interrupted a
 	 * kernel-mode FPU section.
 	 */
-	if (this_cpu_read(in_kernel_fpu)) {
+	if (!this_cpu_read(kernel_fpu_allowed)) {
 		WARN_ON_FPU(!in_hardirq());
 		return false;
 	}
 
 	/*
@@ -437,13 +437,14 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 {
 	if (!irqs_disabled())
 		fpregs_lock();
 
 	WARN_ON_FPU(!irq_fpu_usable());
-	WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
 
-	this_cpu_write(in_kernel_fpu, true);
+	/* Toggle kernel_fpu_allowed to false: */
+	WARN_ON_FPU(!this_cpu_read(kernel_fpu_allowed));
+	this_cpu_write(kernel_fpu_allowed, false);
 
 	if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER)) &&
 	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		set_thread_flag(TIF_NEED_FPU_LOAD);
 		save_fpregs_to_fpstate(x86_task_fpu(current));
@@ -459,13 +460,14 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 }
 EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask);
 
 void kernel_fpu_end(void)
 {
-	WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
+	/* Toggle kernel_fpu_allowed back to true: */
+	WARN_ON_FPU(this_cpu_read(kernel_fpu_allowed));
+	this_cpu_write(kernel_fpu_allowed, true);
 
-	this_cpu_write(in_kernel_fpu, false);
 	if (!irqs_disabled())
 		fpregs_unlock();
 }
 EXPORT_SYMBOL_GPL(kernel_fpu_end);
 
-- 
2.49.0