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s390/maccess: improve s390_kernel_write()

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Use the sturg instruction instead of the stura instruction. This allows to
modify up to eight bytes in a row instead of only four.

For function tracer enabling and disabling this reduces the time needed to
modify the text sections by 50%, since for each mcount call site six bytes
need to be changed.

Also remove the EXTABLE entries, since calls to this function are not
supposed to fail.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2015-03-13 13:13:36 +01:00 committed by Martin Schwidefsky
parent 8a5d8473dd
commit 3c1a3bcea9
1 changed files with 20 additions and 25 deletions
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45
arch/s390/mm/maccess.c
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@ -1,7 +1,7 @@
/*
* Access kernel memory without faulting -- s390 specific implementation.
*
* Copyright IBM Corp. 2009
* Copyright IBM Corp. 2009, 2015
*
* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
*
@ -18,28 +18,25 @@
static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
{
unsigned long count, aligned;
int offset, mask;
int rc = -EFAULT;
unsigned long aligned, offset, count;
char tmp[8];
aligned = (unsigned long) dst & ~3UL;
offset = (unsigned long) dst & 3;
count = min_t(unsigned long, 4 - offset, size);
mask = (0xf << (4 - count)) & 0xf;
mask >>= offset;
aligned = (unsigned long) dst & ~7UL;
offset = (unsigned long) dst & 7UL;
size = min(8UL - offset, size);
count = size - 1;
asm volatile(
" bras 1,0f\n"
" icm 0,0,0(%3)\n"
"0: l 0,0(%1)\n"
" lra %1,0(%1)\n"
"1: ex %2,0(1)\n"
"2: stura 0,%1\n"
" la %0,0\n"
"3:\n"
EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
: "+d" (rc), "+a" (aligned)
: "a" (mask), "a" (src) : "cc", "memory", "0", "1");
return rc ? rc : count;
" mvc 0(1,%4),0(%5)\n"
"0: mvc 0(8,%3),0(%0)\n"
" ex %1,0(1)\n"
" lg %1,0(%3)\n"
" lra %0,0(%0)\n"
" sturg %1,%0\n"
: "+&a" (aligned), "+&a" (count), "=m" (tmp)
: "a" (&tmp), "a" (&tmp[offset]), "a" (src)
: "cc", "memory", "1");
return size;
}
/*
@ -50,8 +47,8 @@ static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t siz
*
* This function writes to kernel memory bypassing DAT and possible page table
* write protection. It writes to the destination using the sturg instruction.
* Therefore we have a read-modify-write sequence: the function reads four
* bytes from destination at a four byte boundary, modifies the bytes
* Therefore we have a read-modify-write sequence: the function reads eight
* bytes from destination at an eight byte boundary, modifies the bytes
* requested and writes the result back in a loop.
*
* Note: this means that this function may not be called concurrently on
@ -60,12 +57,10 @@ static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t siz
*/
void notrace s390_kernel_write(void *dst, const void *src, size_t size)
{
long copied = 0;
long copied;
while (size) {
copied = s390_kernel_write_odd(dst, src, size);
if (copied < 0)
break;
dst += copied;
src += copied;
size -= copied;