For the non VSX version, that's trivial. Just use unsafe_copy_to_user()
instead of __copy_to_user().

For the VSX version, remove the intermediate step through a buffer and
use unsafe_put_user() directly. This generates a far smaller code which
is acceptable to inline, see below:

Standard VSX version:

0000000000000000 <.copy_fpr_to_user>:
   0:	7c 08 02 a6 	mflr    r0
   4:	fb e1 ff f8 	std     r31,-8(r1)
   8:	39 00 00 20 	li      r8,32
   c:	39 24 0b 80 	addi    r9,r4,2944
  10:	7d 09 03 a6 	mtctr   r8
  14:	f8 01 00 10 	std     r0,16(r1)
  18:	f8 21 fe 71 	stdu    r1,-400(r1)
  1c:	39 41 00 68 	addi    r10,r1,104
  20:	e9 09 00 00 	ld      r8,0(r9)
  24:	39 4a 00 08 	addi    r10,r10,8
  28:	39 29 00 10 	addi    r9,r9,16
  2c:	f9 0a 00 00 	std     r8,0(r10)
  30:	42 00 ff f0 	bdnz    20 <.copy_fpr_to_user+0x20>
  34:	e9 24 0d 80 	ld      r9,3456(r4)
  38:	3d 42 00 00 	addis   r10,r2,0
			3a: R_PPC64_TOC16_HA	.toc
  3c:	eb ea 00 00 	ld      r31,0(r10)
			3e: R_PPC64_TOC16_LO_DS	.toc
  40:	f9 21 01 70 	std     r9,368(r1)
  44:	e9 3f 00 00 	ld      r9,0(r31)
  48:	81 29 00 20 	lwz     r9,32(r9)
  4c:	2f 89 00 00 	cmpwi   cr7,r9,0
  50:	40 9c 00 18 	bge     cr7,68 <.copy_fpr_to_user+0x68>
  54:	4c 00 01 2c 	isync
  58:	3d 20 40 00 	lis     r9,16384
  5c:	79 29 07 c6 	rldicr  r9,r9,32,31
  60:	7d 3d 03 a6 	mtspr   29,r9
  64:	4c 00 01 2c 	isync
  68:	38 a0 01 08 	li      r5,264
  6c:	38 81 00 70 	addi    r4,r1,112
  70:	48 00 00 01 	bl      70 <.copy_fpr_to_user+0x70>
			70: R_PPC64_REL24	.__copy_tofrom_user
  74:	60 00 00 00 	nop
  78:	e9 3f 00 00 	ld      r9,0(r31)
  7c:	81 29 00 20 	lwz     r9,32(r9)
  80:	2f 89 00 00 	cmpwi   cr7,r9,0
  84:	40 9c 00 18 	bge     cr7,9c <.copy_fpr_to_user+0x9c>
  88:	4c 00 01 2c 	isync
  8c:	39 20 ff ff 	li      r9,-1
  90:	79 29 00 44 	rldicr  r9,r9,0,1
  94:	7d 3d 03 a6 	mtspr   29,r9
  98:	4c 00 01 2c 	isync
  9c:	38 21 01 90 	addi    r1,r1,400
  a0:	e8 01 00 10 	ld      r0,16(r1)
  a4:	eb e1 ff f8 	ld      r31,-8(r1)
  a8:	7c 08 03 a6 	mtlr    r0
  ac:	4e 80 00 20 	blr

'unsafe' simulated VSX version (The ... are only nops) using
unsafe_copy_fpr_to_user() macro:

unsigned long copy_fpr_to_user(void __user *to,
			       struct task_struct *task)
{
	unsafe_copy_fpr_to_user(to, task, failed);
	return 0;
failed:
	return 1;
}

0000000000000000 <.copy_fpr_to_user>:
   0:	39 00 00 20 	li      r8,32
   4:	39 44 0b 80 	addi    r10,r4,2944
   8:	7d 09 03 a6 	mtctr   r8
   c:	7c 69 1b 78 	mr      r9,r3
...
  20:	e9 0a 00 00 	ld      r8,0(r10)
  24:	f9 09 00 00 	std     r8,0(r9)
  28:	39 4a 00 10 	addi    r10,r10,16
  2c:	39 29 00 08 	addi    r9,r9,8
  30:	42 00 ff f0 	bdnz    20 <.copy_fpr_to_user+0x20>
  34:	e9 24 0d 80 	ld      r9,3456(r4)
  38:	f9 23 01 00 	std     r9,256(r3)
  3c:	38 60 00 00 	li      r3,0
  40:	4e 80 00 20 	blr
...
  50:	38 60 00 01 	li      r3,1
  54:	4e 80 00 20 	blr
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/29f6c4b8e7a5bbc61e6a8801b78bbf493f9f819e.1597770847.git.christophe.leroy@csgroup.eu