linux-kernel - [PATCH 4/5] arm64/fpsimd: Require kernel NEON begin/end calls from the same scope

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Message-ID: <20250918063539.2640512-11-ardb+git@google.com>
Date: Thu, 18 Sep 2025 08:35:44 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	herbert@...dor.apana.org.au, ebiggers@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>
Subject: [PATCH 4/5] arm64/fpsimd: Require kernel NEON begin/end calls from
 the same scope

From: Ard Biesheuvel <ardb@...nel.org>

In preparation for making kernel_neon_begin() allocate a stack based
buffer for stashing the kernel mode FP/SIMD state on a context switch,
redefine kernel_neon_begin() and kernel_neon_end() as macros, in a way
that requires them to be called from the same scope, and therefore,
running from the same stack frame.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/include/asm/neon.h |  7 +++++--
 arch/arm64/kernel/fpsimd.c    | 12 ++++++------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/neon.h b/arch/arm64/include/asm/neon.h
index d4b1d172a79b..4e24f1058b55 100644
--- a/arch/arm64/include/asm/neon.h
+++ b/arch/arm64/include/asm/neon.h
@@ -13,7 +13,10 @@
 
 #define cpu_has_neon()		system_supports_fpsimd()
 
-void kernel_neon_begin(void);
-void kernel_neon_end(void);
+void __kernel_neon_begin(void);
+void __kernel_neon_end(void);
+
+#define kernel_neon_begin()	do { __kernel_neon_begin()
+#define kernel_neon_end()	__kernel_neon_end(); } while (0)
 
 #endif /* ! __ASM_NEON_H */
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index c37f02d7194e..d7eb073d1366 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1833,7 +1833,7 @@ void fpsimd_save_and_flush_cpu_state(void)
  * The caller may freely use the FPSIMD registers until kernel_neon_end() is
  * called.
  */
-void kernel_neon_begin(void)
+void __kernel_neon_begin(void)
 {
 	if (WARN_ON(!system_supports_fpsimd()))
 		return;
@@ -1875,7 +1875,7 @@ void kernel_neon_begin(void)
 
 	put_cpu_fpsimd_context();
 }
-EXPORT_SYMBOL_GPL(kernel_neon_begin);
+EXPORT_SYMBOL_GPL(__kernel_neon_begin);
 
 /*
  * kernel_neon_end(): give the CPU FPSIMD registers back to the current task
@@ -1886,7 +1886,7 @@ EXPORT_SYMBOL_GPL(kernel_neon_begin);
  * The caller must not use the FPSIMD registers after this function is called,
  * unless kernel_neon_begin() is called again in the meantime.
  */
-void kernel_neon_end(void)
+void __kernel_neon_end(void)
 {
 	if (!system_supports_fpsimd())
 		return;
@@ -1902,7 +1902,7 @@ void kernel_neon_end(void)
 	else
 		clear_thread_flag(TIF_KERNEL_FPSTATE);
 }
-EXPORT_SYMBOL_GPL(kernel_neon_end);
+EXPORT_SYMBOL_GPL(__kernel_neon_end);
 
 #ifdef CONFIG_EFI
 
@@ -1936,7 +1936,7 @@ void __efi_fpsimd_begin(void)
 	WARN_ON(preemptible());
 
 	if (may_use_simd()) {
-		kernel_neon_begin();
+		__kernel_neon_begin();
 	} else {
 		/*
 		 * If !efi_sve_state, SVE can't be in use yet and doesn't need
@@ -1985,7 +1985,7 @@ void __efi_fpsimd_end(void)
 		return;
 
 	if (!efi_fpsimd_state_used) {
-		kernel_neon_end();
+		__kernel_neon_end();
 	} else {
 		if (system_supports_sve() && efi_sve_state_used) {
 			bool ffr = true;
-- 
2.51.0.384.g4c02a37b29-goog