[v2] arm64: Move kernel mode FPSIMD buffer to the stack

[PATCH v2 02/20] arm64/simd: Add scoped guard API for kernel mode SIMD

Posted by Ard Biesheuvel 4 months, 1 week ago

From: Ard Biesheuvel <ardb@kernel.org>

Encapsulate kernel_neon_begin() and kernel_neon_end() using a 'ksimd'
cleanup guard. This hides the prototype of those functions, allowing
them to be changed for arm64 but not ARM, without breaking code that is
shared between those architectures (RAID6, AEGIS-128)

It probably makes sense to expose this API more widely across
architectures, as it affords more flexibility to the arch code to
plumb it in, while imposing more rigid rules regarding the start/end
bookends appearing in matched pairs.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/simd.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
index 8e86c9e70e48..d9f83c478736 100644
--- a/arch/arm64/include/asm/simd.h
+++ b/arch/arm64/include/asm/simd.h
@@ -6,12 +6,15 @@
 #ifndef __ASM_SIMD_H
 #define __ASM_SIMD_H
 
+#include <linux/cleanup.h>
 #include <linux/compiler.h>
 #include <linux/irqflags.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/types.h>
 
+#include <asm/neon.h>
+
 #ifdef CONFIG_KERNEL_MODE_NEON
 
 /*
@@ -40,4 +43,8 @@ static __must_check inline bool may_use_simd(void) {
 
 #endif /* ! CONFIG_KERNEL_MODE_NEON */
 
+DEFINE_LOCK_GUARD_0(ksimd, kernel_neon_begin(), kernel_neon_end())
+
+#define scoped_ksimd()	scoped_guard(ksimd)
+
 #endif
-- 
2.51.0.618.g983fd99d29-goog

Re: [PATCH v2 02/20] arm64/simd: Add scoped guard API for kernel mode SIMD

Posted by Mark Brown 3 months, 3 weeks ago

On Wed, Oct 01, 2025 at 11:02:04PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> Encapsulate kernel_neon_begin() and kernel_neon_end() using a 'ksimd'
> cleanup guard. This hides the prototype of those functions, allowing
> them to be changed for arm64 but not ARM, without breaking code that is
> shared between those architectures (RAID6, AEGIS-128)

Reviewed-by: Mark Brown <broonie@kernel.org>

Re: [PATCH v2 02/20] arm64/simd: Add scoped guard API for kernel mode SIMD

Posted by Kees Cook 4 months, 1 week ago

On Wed, Oct 01, 2025 at 11:02:04PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> Encapsulate kernel_neon_begin() and kernel_neon_end() using a 'ksimd'
> cleanup guard. This hides the prototype of those functions, allowing
> them to be changed for arm64 but not ARM, without breaking code that is
> shared between those architectures (RAID6, AEGIS-128)
> 
> It probably makes sense to expose this API more widely across
> architectures, as it affords more flexibility to the arch code to
> plumb it in, while imposing more rigid rules regarding the start/end
> bookends appearing in matched pairs.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook