[PATCH v3 4/4] powerpc/inst: Optimise copy_inst_from_kernel_nofault()

[Christophe Leroy <christophe.leroy@csgroup.eu>]

copy_inst_from_kernel_nofault() uses copy_from_kernel_nofault() to
copy one or two 32bits words. This means calling an out-of-line
function which itself calls back copy_from_kernel_nofault_allowed()
then performs a generic copy with loops.

Rewrite copy_inst_from_kernel_nofault() to do everything at a
single place and use __get_kernel_nofault() directly to perform
single accesses without loops.

Before the patch:

	00000018 <copy_inst_from_kernel_nofault>:
	  18:	94 21 ff e0 	stwu    r1,-32(r1)
	  1c:	7c 08 02 a6 	mflr    r0
	  20:	38 a0 00 04 	li      r5,4
	  24:	93 e1 00 1c 	stw     r31,28(r1)
	  28:	7c 7f 1b 78 	mr      r31,r3
	  2c:	38 61 00 08 	addi    r3,r1,8
	  30:	90 01 00 24 	stw     r0,36(r1)
	  34:	48 00 00 01 	bl      34 <copy_inst_from_kernel_nofault+0x1c>
				34: R_PPC_REL24	copy_from_kernel_nofault
	  38:	2c 03 00 00 	cmpwi   r3,0
	  3c:	40 82 00 0c 	bne     48 <copy_inst_from_kernel_nofault+0x30>
	  40:	81 21 00 08 	lwz     r9,8(r1)
	  44:	91 3f 00 00 	stw     r9,0(r31)
	  48:	80 01 00 24 	lwz     r0,36(r1)
	  4c:	83 e1 00 1c 	lwz     r31,28(r1)
	  50:	38 21 00 20 	addi    r1,r1,32
	  54:	7c 08 03 a6 	mtlr    r0
	  58:	4e 80 00 20 	blr

After the patch:

	00000018 <copy_inst_from_kernel_nofault>:
	  18:	3d 20 b0 00 	lis     r9,-20480
	  1c:	7c 04 48 40 	cmplw   r4,r9
	  20:	7c 69 1b 78 	mr      r9,r3
	  24:	41 80 00 2c 	blt     50 <copy_inst_from_kernel_nofault+0x38>
	  28:	81 42 04 d0 	lwz     r10,1232(r2)
	  2c:	39 4a 00 01 	addi    r10,r10,1
	  30:	91 42 04 d0 	stw     r10,1232(r2)
	  34:	80 e4 00 00 	lwz     r7,0(r4)
	  38:	81 42 04 d0 	lwz     r10,1232(r2)
	  3c:	38 60 00 00 	li      r3,0
	  40:	39 4a ff ff 	addi    r10,r10,-1
	  44:	91 42 04 d0 	stw     r10,1232(r2)
	  48:	90 e9 00 00 	stw     r7,0(r9)
	  4c:	4e 80 00 20 	blr

	  50:	38 60 ff de 	li      r3,-34
	  54:	4e 80 00 20 	blr
	  58:	81 22 04 d0 	lwz     r9,1232(r2)
	  5c:	38 60 ff f2 	li      r3,-14
	  60:	39 29 ff ff 	addi    r9,r9,-1
	  64:	91 22 04 d0 	stw     r9,1232(r2)
	  68:	4e 80 00 20 	blr

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v3: New
---
 arch/powerpc/mm/maccess.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/mm/maccess.c b/arch/powerpc/mm/maccess.c
index 5abae96b2b46..90309806f5eb 100644
--- a/arch/powerpc/mm/maccess.c
+++ b/arch/powerpc/mm/maccess.c
@@ -15,16 +15,22 @@ bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
 int copy_inst_from_kernel_nofault(ppc_inst_t *inst, u32 *src)
 {
 	unsigned int val, suffix;
-	int err;
 
-	err = copy_from_kernel_nofault(&val, src, sizeof(val));
-	if (err)
-		return err;
+	if (unlikely(!is_kernel_addr((unsigned long)src)))
+		return -ERANGE;
+
+	pagefault_disable();
+	__get_kernel_nofault(&val, src, u32, Efault);
 	if (IS_ENABLED(CONFIG_PPC64) && get_op(val) == OP_PREFIX) {
-		err = copy_from_kernel_nofault(&suffix, src + 1, sizeof(suffix));
+		__get_kernel_nofault(&suffix, src + 1, u32, Efault);
+		pagefault_enable();
 		*inst = ppc_inst_prefix(val, suffix);
 	} else {
+		pagefault_enable();
 		*inst = ppc_inst(val);
 	}
-	return err;
+	return 0;
+Efault:
+	pagefault_enable();
+	return -EFAULT;
 }
-- 
2.33.1