diff mbox series

[net-next,v3,01/17] asm: simd context helper API

Message ID 20180911010838.8818-2-Jason@zx2c4.com
State Superseded
Headers show
Series WireGuard: Secure Network Tunnel | expand

Commit Message

Jason A. Donenfeld Sept. 11, 2018, 1:08 a.m. UTC 
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();
    while ((item = get_item_from_queue()) != NULL) {
        encrypt_item(item, simd_context);
        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.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Reviewed-by: Palmer Dabbelt <palmer@sifive.com>

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Samuel Neves <sneves@dei.uc.pt>
Cc: linux-arch@vger.kernel.org
---
 arch/alpha/include/asm/Kbuild      |  5 ++--
 arch/arc/include/asm/Kbuild        |  1 +
 arch/arm/include/asm/simd.h        | 42 ++++++++++++++++++++++++++++++
 arch/arm64/include/asm/simd.h      | 37 +++++++++++++++++++++-----
 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        | 30 ++++++++++++++++++++-
 arch/xtensa/include/asm/Kbuild     |  1 +
 include/asm-generic/simd.h         | 15 +++++++++++
 include/linux/simd.h               | 28 ++++++++++++++++++++
 26 files changed, 180 insertions(+), 21 deletions(-)
 create mode 100644 arch/arm/include/asm/simd.h
 create mode 100644 include/linux/simd.h

-- 
2.18.0

Comments

Kevin Easton Sept. 12, 2018, 6:14 a.m. UTC | #1 
On Mon, Sep 10, 2018 at 07:08:21PM -0600, Jason A. Donenfeld 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();

>     while ((item = get_item_from_queue()) != NULL) {

>         encrypt_item(item, simd_context);

>         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.


Given that it's always supposed to be used like that, mightn't it be
better if simd_relax() took a pointer to the context, so the call is
just

    simd_relax(&simd_context);

?

The inlining means that there won't actually be a pointer dereference in
the emitted code.

If simd_put() also took a pointer then it could set the context back to
HAVE_NO_SIMD as well?

    - Kevin
Jason A. Donenfeld Sept. 12, 2018, 6:10 p.m. UTC | #2 
On Wed, Sep 12, 2018 at 8:14 AM Kevin Easton <kevin@guarana.org> wrote:
> Given that it's always supposed to be used like that, mightn't it be

> better if simd_relax() took a pointer to the context, so the call is

> just

>

>     simd_relax(&simd_context);

>

> ?

>

> The inlining means that there won't actually be a pointer dereference in

> the emitted code.

>

> If simd_put() also took a pointer then it could set the context back to

> HAVE_NO_SIMD as well?


That's sort of a neat idea. I guess in this scheme, you'd envision:

   simd_context_t simd_context;

   simd_get(&simd_context);
   simd_relax(&simd_context);
   simd_put(&simd_context);

And this way, if simd_context ever becomes a heavier struct, it can be
modified in place rather than returned by value from the function. On
the other hand, it's a little bit more annoying to type and makes it
harder to do declaration and initialization on the same line.
Kevin Easton Sept. 13, 2018, 5:03 a.m. UTC | #3 
On Wed, Sep 12, 2018 at 08:10:41PM +0200, Jason A. Donenfeld wrote:
> On Wed, Sep 12, 2018 at 8:14 AM Kevin Easton <kevin@guarana.org> wrote:

> > Given that it's always supposed to be used like that, mightn't it be

> > better if simd_relax() took a pointer to the context, so the call is

> > just

> >

> >     simd_relax(&simd_context);

> >

> > ?

> >

> > The inlining means that there won't actually be a pointer dereference in

> > the emitted code.

> >

> > If simd_put() also took a pointer then it could set the context back to

> > HAVE_NO_SIMD as well?

> 

> That's sort of a neat idea. I guess in this scheme, you'd envision:

> 

>    simd_context_t simd_context;

> 

>    simd_get(&simd_context);

>    simd_relax(&simd_context);

>    simd_put(&simd_context);

> 

> And this way, if simd_context ever becomes a heavier struct, it can be

> modified in place rather than returned by value from the function. On

> the other hand, it's a little bit more annoying to type and makes it

> harder to do declaration and initialization on the same line.


Yes.  It's also how most get/put APIs already work in the kernel, eg
kref_get/put (mostly because they tend to be 'getting/putting' an
already-initialized object, though).

    - Kevin
Jason A. Donenfeld Sept. 13, 2018, 1:52 p.m. UTC | #4 
On Thu, Sep 13, 2018 at 7:03 AM Kevin Easton <kevin@guarana.org> wrote:
> Yes.  It's also how most get/put APIs already work in the kernel, eg

> kref_get/put (mostly because they tend to be 'getting/putting' an

> already-initialized object, though).


Right; in this case the object wouldn't be initialized yet, which
might defeat the purpose, since one advantage of the & way you
mentioned is _put modifies the context.

Andy - any opinions on this? The tl;dr is:

1) what we have now:

simd_context_t simd_context = simd_get();
for (item in items) {
    do_something(item);
    simd_context = simd_relax(simd_context);
}
simd_put();

2) what kevin is proposing:

simd_context_t simd_context;

simd_get(&simd_context);
for (item in items) {
    do_something(item);
    simd_relax(&simd_context);
}
simd_put(&simd_context);

I can see pros and cons of each approach.
Jason A. Donenfeld Sept. 13, 2018, 1:53 p.m. UTC | #5 
On Thu, Sep 13, 2018 at 3:52 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> simd_put();

Rather, simd_put(simd_context);
Jason A. Donenfeld Sept. 15, 2018, 8:01 p.m. UTC | #6 
On Sat, Sep 15, 2018 at 9:58 PM Andy Lutomirski <luto@amacapital.net> wrote:
> I have no strong opinion, except that, if you paint the bikeshed “pass by value”, then simd_get and simd_relax should probably have warn_unused_result set.


Good idea.
Jason A. Donenfeld Sept. 17, 2018, 1:14 p.m. UTC | #7 
Hey Kevin,

I found numerous other advantages in doing it the way you suggested
(which also helped squash some bugs), and so this will be part of v5.
Thanks for the suggestion.

Regards,
Jason
diff mbox series

Patch

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..bf468993bbef
--- /dev/null
+++ b/arch/arm/include/asm/simd.h
@@ -0,0 +1,42 @@ 
+/* 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
+
+static __must_check inline bool may_use_simd(void)
+{
+	return !in_interrupt();
+}
+
+#ifdef CONFIG_KERNEL_MODE_NEON
+#include <asm/neon.h>
+
+static inline simd_context_t simd_get(void)
+{
+	bool have_simd = may_use_simd();
+	if (have_simd)
+		kernel_neon_begin();
+	return have_simd ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+	if (prior_context != HAVE_NO_SIMD)
+		kernel_neon_end();
+}
+#else
+static inline simd_context_t simd_get(void)
+{
+	return HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+}
+#endif
+
+#endif /* _ASM_SIMD_H */
diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
index 6495cc51246f..058c336de38d 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);
 
@@ -40,12 +41,36 @@  static __must_check inline bool may_use_simd(void)
 		!this_cpu_read(kernel_neon_busy);
 }
 
+static inline simd_context_t simd_get(void)
+{
+	bool have_simd = may_use_simd();
+	if (have_simd)
+		kernel_neon_begin();
+	return have_simd ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+	if (prior_context != HAVE_NO_SIMD)
+		kernel_neon_end();
+}
+
 #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 simd_context_t simd_get(void)
+{
+	return HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+}
+
 #endif /* ! CONFIG_KERNEL_MODE_NEON */
 
 #endif
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..79411178988a 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 +17,24 @@  static __must_check inline bool may_use_simd(void)
 {
 	return irq_fpu_usable();
 }
+
+static inline simd_context_t simd_get(void)
+{
+	bool have_simd = false;
+#if !defined(CONFIG_UML)
+	have_simd = may_use_simd();
+	if (have_simd)
+		kernel_fpu_begin();
+#endif
+	return have_simd ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+#if !defined(CONFIG_UML)
+	if (prior_context != HAVE_NO_SIMD)
+		kernel_fpu_end();
+#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..fad899a5a92d 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 +17,14 @@  static __must_check inline bool may_use_simd(void)
 {
 	return !in_interrupt();
 }
+
+static inline simd_context_t simd_get(void)
+{
+	return HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t prior_context)
+{
+}
+
+#endif /* _ASM_SIMD_H */
diff --git a/include/linux/simd.h b/include/linux/simd.h
new file mode 100644
index 000000000000..f62d047188bf
--- /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,
+	HAVE_FULL_SIMD
+} simd_context_t;
+
+#include <linux/sched.h>
+#include <asm/simd.h>
+
+static inline simd_context_t simd_relax(simd_context_t prior_context)
+{
+#ifdef CONFIG_PREEMPT
+	if (prior_context != HAVE_NO_SIMD && need_resched()) {
+		simd_put(prior_context);
+		return simd_get();
+	}
+#endif
+	return prior_context;
+}
+
+#endif /* _SIMD_H */