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4fa617cc68
Commit aefbab8e77
("arm64: fpsimd: Preserve/restore kernel mode NEON at context switch")
added a 'kernel_fpsimd_state' field to struct thread_struct, which is
the arch-specific portion of struct task_struct, and is allocated for
each task in the system. The size of this field is 528 bytes, resulting
in non-negligible bloat of task_struct, and the resulting memory
overhead may impact performance on systems with many processes.
This allocation is only used if the task is scheduled out or interrupted
by a softirq while using the FP/SIMD unit in kernel mode, and so it is
possible to transparently allocate this buffer on the caller's stack
instead.
So tweak the 'ksimd' scoped guard implementation so that a stack buffer
is allocated and passed to both kernel_neon_begin() and
kernel_neon_end(), and either record it in the task struct, or use it
directly to preserve the task mode kernel FP/SIMD when running in
softirq context. Passing the address to both functions, and checking the
addresses for consistency ensures that callers of the updated bare
begin/end API use it in a manner that is consistent with the new context
switch semantics.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
28 lines
448 B
C
28 lines
448 B
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2023 SiFive
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*/
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#ifndef __ASM_FPU_H
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#define __ASM_FPU_H
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#include <linux/preempt.h>
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#include <asm/neon.h>
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#define kernel_fpu_available() cpu_has_neon()
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static inline void kernel_fpu_begin(void)
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{
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BUG_ON(!in_task());
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preempt_disable();
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kernel_neon_begin(NULL);
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}
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static inline void kernel_fpu_end(void)
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{
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kernel_neon_end(NULL);
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preempt_enable();
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}
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#endif /* ! __ASM_FPU_H */
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