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    Subject[PATCH net-next v6 01/23] asm: simd context helper API
    Date
    Sometimes it's useful to amortize calls to XSAVE/XRSTOR and the related
    FPU/SIMD functions over a number of calls, because FPU restoration is
    quite expensive. This adds a simple header for carrying out this pattern:

    simd_context_t simd_context;

    simd_get(&simd_context);
    while ((item = get_item_from_queue()) != NULL) {
    encrypt_item(item, simd_context);
    simd_relax(&simd_context);
    }
    simd_put(&simd_context);

    The relaxation step ensures that we don't trample over preemption, and
    the get/put API should be a familiar paradigm in the kernel.

    On the other end, code that actually wants to use SIMD instructions can
    accept this as a parameter and check it via:

    void encrypt_item(struct item *item, simd_context_t *simd_context)
    {
    if (item->len > LARGE_FOR_SIMD && simd_use(simd_context))
    wild_simd_code(item);
    else
    boring_scalar_code(item);
    }

    The actual XSAVE happens during simd_use (and only on the first time),
    so that if the context is never actually used, no performance penalty is
    hit.

    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Cc: Samuel Neves <sneves@dei.uc.pt>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: linux-arch@vger.kernel.org
    ---
    arch/alpha/include/asm/Kbuild | 5 ++-
    arch/arc/include/asm/Kbuild | 1 +
    arch/arm/include/asm/simd.h | 63 ++++++++++++++++++++++++++++++
    arch/arm64/include/asm/simd.h | 51 +++++++++++++++++++++---
    arch/c6x/include/asm/Kbuild | 3 +-
    arch/h8300/include/asm/Kbuild | 3 +-
    arch/hexagon/include/asm/Kbuild | 1 +
    arch/ia64/include/asm/Kbuild | 1 +
    arch/m68k/include/asm/Kbuild | 1 +
    arch/microblaze/include/asm/Kbuild | 1 +
    arch/mips/include/asm/Kbuild | 1 +
    arch/nds32/include/asm/Kbuild | 7 ++--
    arch/nios2/include/asm/Kbuild | 1 +
    arch/openrisc/include/asm/Kbuild | 7 ++--
    arch/parisc/include/asm/Kbuild | 1 +
    arch/powerpc/include/asm/Kbuild | 3 +-
    arch/riscv/include/asm/Kbuild | 3 +-
    arch/s390/include/asm/Kbuild | 3 +-
    arch/sh/include/asm/Kbuild | 1 +
    arch/sparc/include/asm/Kbuild | 1 +
    arch/um/include/asm/Kbuild | 3 +-
    arch/unicore32/include/asm/Kbuild | 1 +
    arch/x86/include/asm/simd.h | 44 ++++++++++++++++++++-
    arch/xtensa/include/asm/Kbuild | 1 +
    include/asm-generic/simd.h | 20 ++++++++++
    include/linux/simd.h | 28 +++++++++++++
    26 files changed, 234 insertions(+), 21 deletions(-)
    create mode 100644 arch/arm/include/asm/simd.h
    create mode 100644 include/linux/simd.h

    diff --git a/arch/alpha/include/asm/Kbuild b/arch/alpha/include/asm/Kbuild
    index 0580cb8c84b2..07b2c1025d34 100644
    --- a/arch/alpha/include/asm/Kbuild
    +++ b/arch/alpha/include/asm/Kbuild
    @@ -2,14 +2,15 @@


    generic-y += compat.h
    +generic-y += current.h
    generic-y += exec.h
    generic-y += export.h
    generic-y += fb.h
    generic-y += irq_work.h
    +generic-y += kprobes.h
    generic-y += mcs_spinlock.h
    generic-y += mm-arch-hooks.h
    generic-y += preempt.h
    generic-y += sections.h
    +generic-y += simd.h
    generic-y += trace_clock.h
    -generic-y += current.h
    -generic-y += kprobes.h
    diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
    index feed50ce89fa..a7f4255f1649 100644
    --- a/arch/arc/include/asm/Kbuild
    +++ b/arch/arc/include/asm/Kbuild
    @@ -22,6 +22,7 @@ generic-y += parport.h
    generic-y += pci.h
    generic-y += percpu.h
    generic-y += preempt.h
    +generic-y += simd.h
    generic-y += topology.h
    generic-y += trace_clock.h
    generic-y += user.h
    diff --git a/arch/arm/include/asm/simd.h b/arch/arm/include/asm/simd.h
    new file mode 100644
    index 000000000000..263950dd69cb
    --- /dev/null
    +++ b/arch/arm/include/asm/simd.h
    @@ -0,0 +1,63 @@
    +/* SPDX-License-Identifier: GPL-2.0
    + *
    + * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
    + */
    +
    +#include <linux/simd.h>
    +#ifndef _ASM_SIMD_H
    +#define _ASM_SIMD_H
    +
    +#ifdef CONFIG_KERNEL_MODE_NEON
    +#include <asm/neon.h>
    +
    +static __must_check inline bool may_use_simd(void)
    +{
    + return !in_interrupt();
    +}
    +
    +static inline void simd_get(simd_context_t *ctx)
    +{
    + *ctx = may_use_simd() ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    + if (*ctx & HAVE_SIMD_IN_USE)
    + kernel_neon_end();
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    + if (!(*ctx & HAVE_FULL_SIMD))
    + return false;
    + if (*ctx & HAVE_SIMD_IN_USE)
    + return true;
    + kernel_neon_begin();
    + *ctx |= HAVE_SIMD_IN_USE;
    + return true;
    +}
    +
    +#else
    +
    +static __must_check inline bool may_use_simd(void)
    +{
    + return false;
    +}
    +
    +static inline void simd_get(simd_context_t *ctx)
    +{
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    + return false;
    +}
    +#endif
    +
    +#endif /* _ASM_SIMD_H */
    diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
    index 6495cc51246f..a45ff1600040 100644
    --- a/arch/arm64/include/asm/simd.h
    +++ b/arch/arm64/include/asm/simd.h
    @@ -1,11 +1,10 @@
    -/*
    - * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
    +/* SPDX-License-Identifier: GPL-2.0
    *
    - * This program is free software; you can redistribute it and/or modify it
    - * under the terms of the GNU General Public License version 2 as published
    - * by the Free Software Foundation.
    + * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
    + * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
    */

    +#include <linux/simd.h>
    #ifndef __ASM_SIMD_H
    #define __ASM_SIMD_H

    @@ -16,6 +15,8 @@
    #include <linux/types.h>

    #ifdef CONFIG_KERNEL_MODE_NEON
    +#include <asm/neon.h>
    +#include <asm/simd.h>

    DECLARE_PER_CPU(bool, kernel_neon_busy);

    @@ -40,9 +41,47 @@ static __must_check inline bool may_use_simd(void)
    !this_cpu_read(kernel_neon_busy);
    }

    +static inline void simd_get(simd_context_t *ctx)
    +{
    + *ctx = may_use_simd() ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    + if (*ctx & HAVE_SIMD_IN_USE)
    + kernel_neon_end();
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    + if (!(*ctx & HAVE_FULL_SIMD))
    + return false;
    + if (*ctx & HAVE_SIMD_IN_USE)
    + return true;
    + kernel_neon_begin();
    + *ctx |= HAVE_SIMD_IN_USE;
    + return true;
    +}
    +
    #else /* ! CONFIG_KERNEL_MODE_NEON */

    -static __must_check inline bool may_use_simd(void) {
    +static __must_check inline bool may_use_simd(void)
    +{
    + return false;
    +}
    +
    +static inline void simd_get(simd_context_t *ctx)
    +{
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    return false;
    }

    diff --git a/arch/c6x/include/asm/Kbuild b/arch/c6x/include/asm/Kbuild
    index 33a2c94fed0d..22f3d8333c74 100644
    --- a/arch/c6x/include/asm/Kbuild
    +++ b/arch/c6x/include/asm/Kbuild
    @@ -5,8 +5,8 @@ generic-y += compat.h
    generic-y += current.h
    generic-y += device.h
    generic-y += div64.h
    -generic-y += dma.h
    generic-y += dma-mapping.h
    +generic-y += dma.h
    generic-y += emergency-restart.h
    generic-y += exec.h
    generic-y += extable.h
    @@ -30,6 +30,7 @@ generic-y += pgalloc.h
    generic-y += preempt.h
    generic-y += segment.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += tlbflush.h
    generic-y += topology.h
    generic-y += trace_clock.h
    diff --git a/arch/h8300/include/asm/Kbuild b/arch/h8300/include/asm/Kbuild
    index a5d0b2991f47..f5c2f12d593e 100644
    --- a/arch/h8300/include/asm/Kbuild
    +++ b/arch/h8300/include/asm/Kbuild
    @@ -8,8 +8,8 @@ generic-y += current.h
    generic-y += delay.h
    generic-y += device.h
    generic-y += div64.h
    -generic-y += dma.h
    generic-y += dma-mapping.h
    +generic-y += dma.h
    generic-y += emergency-restart.h
    generic-y += exec.h
    generic-y += extable.h
    @@ -39,6 +39,7 @@ generic-y += preempt.h
    generic-y += scatterlist.h
    generic-y += sections.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += sizes.h
    generic-y += spinlock.h
    generic-y += timex.h
    diff --git a/arch/hexagon/include/asm/Kbuild b/arch/hexagon/include/asm/Kbuild
    index dd2fd9c0d292..217d4695fd8a 100644
    --- a/arch/hexagon/include/asm/Kbuild
    +++ b/arch/hexagon/include/asm/Kbuild
    @@ -29,6 +29,7 @@ generic-y += rwsem.h
    generic-y += sections.h
    generic-y += segment.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += sizes.h
    generic-y += topology.h
    generic-y += trace_clock.h
    diff --git a/arch/ia64/include/asm/Kbuild b/arch/ia64/include/asm/Kbuild
    index 557bbc8ba9f5..41c5ebdf79e5 100644
    --- a/arch/ia64/include/asm/Kbuild
    +++ b/arch/ia64/include/asm/Kbuild
    @@ -4,6 +4,7 @@ generic-y += irq_work.h
    generic-y += mcs_spinlock.h
    generic-y += mm-arch-hooks.h
    generic-y += preempt.h
    +generic-y += simd.h
    generic-y += trace_clock.h
    generic-y += vtime.h
    generic-y += word-at-a-time.h
    diff --git a/arch/m68k/include/asm/Kbuild b/arch/m68k/include/asm/Kbuild
    index a4b8d3331a9e..73898dd1a4d0 100644
    --- a/arch/m68k/include/asm/Kbuild
    +++ b/arch/m68k/include/asm/Kbuild
    @@ -19,6 +19,7 @@ generic-y += mm-arch-hooks.h
    generic-y += percpu.h
    generic-y += preempt.h
    generic-y += sections.h
    +generic-y += simd.h
    generic-y += spinlock.h
    generic-y += topology.h
    generic-y += trace_clock.h
    diff --git a/arch/microblaze/include/asm/Kbuild b/arch/microblaze/include/asm/Kbuild
    index 569ba9e670c1..7a877eea99d3 100644
    --- a/arch/microblaze/include/asm/Kbuild
    +++ b/arch/microblaze/include/asm/Kbuild
    @@ -25,6 +25,7 @@ generic-y += parport.h
    generic-y += percpu.h
    generic-y += preempt.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += syscalls.h
    generic-y += topology.h
    generic-y += trace_clock.h
    diff --git a/arch/mips/include/asm/Kbuild b/arch/mips/include/asm/Kbuild
    index 58351e48421e..e8868e0fb2c3 100644
    --- a/arch/mips/include/asm/Kbuild
    +++ b/arch/mips/include/asm/Kbuild
    @@ -16,6 +16,7 @@ generic-y += qrwlock.h
    generic-y += qspinlock.h
    generic-y += sections.h
    generic-y += segment.h
    +generic-y += simd.h
    generic-y += trace_clock.h
    generic-y += unaligned.h
    generic-y += user.h
    diff --git a/arch/nds32/include/asm/Kbuild b/arch/nds32/include/asm/Kbuild
    index dbc4e5422550..603c1d020620 100644
    --- a/arch/nds32/include/asm/Kbuild
    +++ b/arch/nds32/include/asm/Kbuild
    @@ -7,14 +7,14 @@ generic-y += bug.h
    generic-y += bugs.h
    generic-y += checksum.h
    generic-y += clkdev.h
    -generic-y += cmpxchg.h
    generic-y += cmpxchg-local.h
    +generic-y += cmpxchg.h
    generic-y += compat.h
    generic-y += cputime.h
    generic-y += device.h
    generic-y += div64.h
    -generic-y += dma.h
    generic-y += dma-mapping.h
    +generic-y += dma.h
    generic-y += emergency-restart.h
    generic-y += errno.h
    generic-y += exec.h
    @@ -46,14 +46,15 @@ generic-y += sections.h
    generic-y += segment.h
    generic-y += serial.h
    generic-y += shmbuf.h
    +generic-y += simd.h
    generic-y += sizes.h
    generic-y += stat.h
    generic-y += switch_to.h
    generic-y += timex.h
    generic-y += topology.h
    generic-y += trace_clock.h
    -generic-y += xor.h
    generic-y += unaligned.h
    generic-y += user.h
    generic-y += vga.h
    generic-y += word-at-a-time.h
    +generic-y += xor.h
    diff --git a/arch/nios2/include/asm/Kbuild b/arch/nios2/include/asm/Kbuild
    index 8fde4fa2c34f..571a9d9ad107 100644
    --- a/arch/nios2/include/asm/Kbuild
    +++ b/arch/nios2/include/asm/Kbuild
    @@ -33,6 +33,7 @@ generic-y += preempt.h
    generic-y += sections.h
    generic-y += segment.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += spinlock.h
    generic-y += topology.h
    generic-y += trace_clock.h
    diff --git a/arch/openrisc/include/asm/Kbuild b/arch/openrisc/include/asm/Kbuild
    index eb87cd8327c8..5e9f2f4c4d39 100644
    --- a/arch/openrisc/include/asm/Kbuild
    +++ b/arch/openrisc/include/asm/Kbuild
    @@ -28,12 +28,13 @@ generic-y += module.h
    generic-y += pci.h
    generic-y += percpu.h
    generic-y += preempt.h
    -generic-y += qspinlock_types.h
    -generic-y += qspinlock.h
    -generic-y += qrwlock_types.h
    generic-y += qrwlock.h
    +generic-y += qrwlock_types.h
    +generic-y += qspinlock.h
    +generic-y += qspinlock_types.h
    generic-y += sections.h
    generic-y += segment.h
    +generic-y += simd.h
    generic-y += string.h
    generic-y += switch_to.h
    generic-y += topology.h
    diff --git a/arch/parisc/include/asm/Kbuild b/arch/parisc/include/asm/Kbuild
    index 2013d639e735..97970b4d05ab 100644
    --- a/arch/parisc/include/asm/Kbuild
    +++ b/arch/parisc/include/asm/Kbuild
    @@ -17,6 +17,7 @@ generic-y += percpu.h
    generic-y += preempt.h
    generic-y += seccomp.h
    generic-y += segment.h
    +generic-y += simd.h
    generic-y += topology.h
    generic-y += trace_clock.h
    generic-y += user.h
    diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild
    index 3196d227e351..64290f48e733 100644
    --- a/arch/powerpc/include/asm/Kbuild
    +++ b/arch/powerpc/include/asm/Kbuild
    @@ -4,7 +4,8 @@ generic-y += irq_regs.h
    generic-y += irq_work.h
    generic-y += local64.h
    generic-y += mcs_spinlock.h
    +generic-y += msi.h
    generic-y += preempt.h
    generic-y += rwsem.h
    +generic-y += simd.h
    generic-y += vtime.h
    -generic-y += msi.h
    diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
    index efdbe311e936..6669b7374c0a 100644
    --- a/arch/riscv/include/asm/Kbuild
    +++ b/arch/riscv/include/asm/Kbuild
    @@ -5,9 +5,9 @@ generic-y += compat.h
    generic-y += cputime.h
    generic-y += device.h
    generic-y += div64.h
    -generic-y += dma.h
    generic-y += dma-contiguous.h
    generic-y += dma-mapping.h
    +generic-y += dma.h
    generic-y += emergency-restart.h
    generic-y += errno.h
    generic-y += exec.h
    @@ -46,6 +46,7 @@ generic-y += setup.h
    generic-y += shmbuf.h
    generic-y += shmparam.h
    generic-y += signal.h
    +generic-y += simd.h
    generic-y += socket.h
    generic-y += sockios.h
    generic-y += stat.h
    diff --git a/arch/s390/include/asm/Kbuild b/arch/s390/include/asm/Kbuild
    index e3239772887a..7a26dc6ce815 100644
    --- a/arch/s390/include/asm/Kbuild
    +++ b/arch/s390/include/asm/Kbuild
    @@ -7,9 +7,9 @@ generated-y += unistd_nr.h
    generic-y += asm-offsets.h
    generic-y += cacheflush.h
    generic-y += device.h
    +generic-y += div64.h
    generic-y += dma-contiguous.h
    generic-y += dma-mapping.h
    -generic-y += div64.h
    generic-y += emergency-restart.h
    generic-y += export.h
    generic-y += fb.h
    @@ -22,6 +22,7 @@ generic-y += mcs_spinlock.h
    generic-y += mm-arch-hooks.h
    generic-y += preempt.h
    generic-y += rwsem.h
    +generic-y += simd.h
    generic-y += trace_clock.h
    generic-y += unaligned.h
    generic-y += word-at-a-time.h
    diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
    index 6a5609a55965..8e64ff35a933 100644
    --- a/arch/sh/include/asm/Kbuild
    +++ b/arch/sh/include/asm/Kbuild
    @@ -16,6 +16,7 @@ generic-y += percpu.h
    generic-y += preempt.h
    generic-y += rwsem.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += sizes.h
    generic-y += trace_clock.h
    generic-y += xor.h
    diff --git a/arch/sparc/include/asm/Kbuild b/arch/sparc/include/asm/Kbuild
    index 410b263ef5c8..72b9e08fb350 100644
    --- a/arch/sparc/include/asm/Kbuild
    +++ b/arch/sparc/include/asm/Kbuild
    @@ -17,5 +17,6 @@ generic-y += msi.h
    generic-y += preempt.h
    generic-y += rwsem.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += trace_clock.h
    generic-y += word-at-a-time.h
    diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
    index b10dde6cb793..d37288b08dd2 100644
    --- a/arch/um/include/asm/Kbuild
    +++ b/arch/um/include/asm/Kbuild
    @@ -16,15 +16,16 @@ generic-y += io.h
    generic-y += irq_regs.h
    generic-y += irq_work.h
    generic-y += kdebug.h
    +generic-y += kprobes.h
    generic-y += mcs_spinlock.h
    generic-y += mm-arch-hooks.h
    generic-y += param.h
    generic-y += pci.h
    generic-y += percpu.h
    generic-y += preempt.h
    +generic-y += simd.h
    generic-y += switch_to.h
    generic-y += topology.h
    generic-y += trace_clock.h
    generic-y += word-at-a-time.h
    generic-y += xor.h
    -generic-y += kprobes.h
    diff --git a/arch/unicore32/include/asm/Kbuild b/arch/unicore32/include/asm/Kbuild
    index bfc7abe77905..98a908720bbd 100644
    --- a/arch/unicore32/include/asm/Kbuild
    +++ b/arch/unicore32/include/asm/Kbuild
    @@ -27,6 +27,7 @@ generic-y += preempt.h
    generic-y += sections.h
    generic-y += segment.h
    generic-y += serial.h
    +generic-y += simd.h
    generic-y += sizes.h
    generic-y += syscalls.h
    generic-y += topology.h
    diff --git a/arch/x86/include/asm/simd.h b/arch/x86/include/asm/simd.h
    index a341c878e977..4aad7f158dcb 100644
    --- a/arch/x86/include/asm/simd.h
    +++ b/arch/x86/include/asm/simd.h
    @@ -1,4 +1,11 @@
    -/* SPDX-License-Identifier: GPL-2.0 */
    +/* SPDX-License-Identifier: GPL-2.0
    + *
    + * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
    + */
    +
    +#include <linux/simd.h>
    +#ifndef _ASM_SIMD_H
    +#define _ASM_SIMD_H

    #include <asm/fpu/api.h>

    @@ -10,3 +17,38 @@ static __must_check inline bool may_use_simd(void)
    {
    return irq_fpu_usable();
    }
    +
    +static inline void simd_get(simd_context_t *ctx)
    +{
    +#if !defined(CONFIG_UML)
    + *ctx = may_use_simd() ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
    +#else
    + *ctx = HAVE_NO_SIMD;
    +#endif
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    +#if !defined(CONFIG_UML)
    + if (*ctx & HAVE_SIMD_IN_USE)
    + kernel_fpu_end();
    +#endif
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    +#if !defined(CONFIG_UML)
    + if (!(*ctx & HAVE_FULL_SIMD))
    + return false;
    + if (*ctx & HAVE_SIMD_IN_USE)
    + return true;
    + kernel_fpu_begin();
    + *ctx |= HAVE_SIMD_IN_USE;
    + return true;
    +#else
    + return false;
    +#endif
    +}
    +
    +#endif /* _ASM_SIMD_H */
    diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild
    index 82c756431b49..7950f359649d 100644
    --- a/arch/xtensa/include/asm/Kbuild
    +++ b/arch/xtensa/include/asm/Kbuild
    @@ -24,6 +24,7 @@ generic-y += percpu.h
    generic-y += preempt.h
    generic-y += rwsem.h
    generic-y += sections.h
    +generic-y += simd.h
    generic-y += topology.h
    generic-y += trace_clock.h
    generic-y += word-at-a-time.h
    diff --git a/include/asm-generic/simd.h b/include/asm-generic/simd.h
    index d0343d58a74a..b3dd61ac010e 100644
    --- a/include/asm-generic/simd.h
    +++ b/include/asm-generic/simd.h
    @@ -1,5 +1,9 @@
    /* SPDX-License-Identifier: GPL-2.0 */

    +#include <linux/simd.h>
    +#ifndef _ASM_SIMD_H
    +#define _ASM_SIMD_H
    +
    #include <linux/hardirq.h>

    /*
    @@ -13,3 +17,19 @@ static __must_check inline bool may_use_simd(void)
    {
    return !in_interrupt();
    }
    +
    +static inline void simd_get(simd_context_t *ctx)
    +{
    + *ctx = HAVE_NO_SIMD;
    +}
    +
    +static inline void simd_put(simd_context_t *ctx)
    +{
    +}
    +
    +static __must_check inline bool simd_use(simd_context_t *ctx)
    +{
    + return false;
    +}
    +
    +#endif /* _ASM_SIMD_H */
    diff --git a/include/linux/simd.h b/include/linux/simd.h
    new file mode 100644
    index 000000000000..33bba21012ff
    --- /dev/null
    +++ b/include/linux/simd.h
    @@ -0,0 +1,28 @@
    +/* SPDX-License-Identifier: GPL-2.0
    + *
    + * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
    + */
    +
    +#ifndef _SIMD_H
    +#define _SIMD_H
    +
    +typedef enum {
    + HAVE_NO_SIMD = 1 << 0,
    + HAVE_FULL_SIMD = 1 << 1,
    + HAVE_SIMD_IN_USE = 1 << 31
    +} simd_context_t;
    +
    +#include <linux/sched.h>
    +#include <asm/simd.h>
    +
    +static inline void simd_relax(simd_context_t *ctx)
    +{
    +#ifdef CONFIG_PREEMPT
    + if ((*ctx & HAVE_SIMD_IN_USE) && need_resched()) {
    + simd_put(ctx);
    + simd_get(ctx);
    + }
    +#endif
    +}
    +
    +#endif /* _SIMD_H */
    --
    2.19.0
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