s390/maccess: improve s390_kernel_write()
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>
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index fb737e9..8a993a5 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -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 @@
*
* 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 @@
*/
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;