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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>
54 lines
1.3 KiB
C
54 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
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*/
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#ifndef __ASM_SIMD_H
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#define __ASM_SIMD_H
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#include <linux/cleanup.h>
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#include <linux/compiler.h>
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#include <linux/irqflags.h>
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#include <linux/percpu.h>
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#include <linux/preempt.h>
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#include <linux/types.h>
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#include <asm/neon.h>
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#ifdef CONFIG_KERNEL_MODE_NEON
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/*
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* may_use_simd - whether it is allowable at this time to issue SIMD
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* instructions or access the SIMD register file
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*
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* Callers must not assume that the result remains true beyond the next
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* preempt_enable() or return from softirq context.
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*/
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static __must_check inline bool may_use_simd(void)
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{
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/*
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* We must make sure that the SVE has been initialized properly
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* before using the SIMD in kernel.
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*/
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return !WARN_ON(!system_capabilities_finalized()) &&
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system_supports_fpsimd() &&
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!in_hardirq() && !irqs_disabled() && !in_nmi();
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}
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#else /* ! CONFIG_KERNEL_MODE_NEON */
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static __must_check inline bool may_use_simd(void) {
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return false;
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}
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#endif /* ! CONFIG_KERNEL_MODE_NEON */
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DEFINE_LOCK_GUARD_1(ksimd,
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struct user_fpsimd_state,
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kernel_neon_begin(_T->lock),
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kernel_neon_end(_T->lock))
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#define scoped_ksimd() scoped_guard(ksimd, &(struct user_fpsimd_state){})
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#endif
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