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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Fri, 28 Sep 2018 10:28:14 +0200
Message-ID: <CAKv+Gu9e35+AyktmSq9qeNE0LR83_yrEEB3DiQv0bmyArivqRQ@mail.gmail.com>
Subject: Re: [PATCH net-next v6 01/23] asm: simd context helper API
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "<netdev@vger.kernel.org>" <netdev@vger.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Samuel Neves <sneves@dei.uc.pt>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arch <linux-arch@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 25 September 2018 at 16:56, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> 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

Given that this patch applies to all architectures at once, it is
probably better to drop the unrelated reordering hunks to avoid
conflicts.

> 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();
> +}
> +

Remember this guy?

https://marc.info/?l=linux-arch&m=149631094625176&w=2

That was never merged, so let's get it right this time.

> +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

Could we return a bool here indicating whether we rescheduled or not?
In some cases, we could pass that into the asm code as a 'reload'
param, allowing repeated loads of key schedules, round constant tables
or S-boxes to be elided.

> +}
> +
> +#endif /* _SIMD_H */
> --
> 2.19.0
>