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s390: introduce CPU alternatives

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Implement CPU alternatives, which allows to optionally patch newer
instructions at runtime, based on CPU facilities availability.

A new kernel boot parameter "noaltinstr" disables patching.

Current implementation is derived from x86 alternatives. Although
ideal instructions padding (when altinstr is longer then oldinstr)
is added at compile time, and no oldinstr nops optimization has to be
done at runtime. Also couple of compile time sanity checks are done:
1. oldinstr and altinstr must be <= 254 bytes long,
2. oldinstr and altinstr must not have an odd length.

alternative(oldinstr, altinstr, facility);
alternative_2(oldinstr, altinstr1, facility1, altinstr2, facility2);

Both compile time and runtime padding consists of either 6/4/2 bytes nop
or a jump (brcl) + 2 bytes nop filler if padding is longer then 6 bytes.

.altinstructions and .altinstr_replacement sections are part of
__init_begin : __init_end region and are freed after initialization.

Signed-off-by: Vasily Gorbik <gor@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Vasily Gorbik
2017-10-12 13:01:47 +02:00
committed by Martin Schwidefsky
parent 76b3b62ade
commit 686140a1a9
8 changed files with 337 additions and 0 deletions
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17
arch/s390/kernel/module.c
View File

@ -31,6 +31,7 @@
#include <linux/kernel.h>
#include <linux/moduleloader.h>
#include <linux/bug.h>
#include <asm/alternative.h>
#if 0
#define DEBUGP printk
@ -429,6 +430,22 @@ int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)
{
const Elf_Shdr *s;
char *secstrings;
if (IS_ENABLED(CONFIG_ALTERNATIVES)) {
secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
if (!strcmp(".altinstructions",
secstrings + s->sh_name)) {
/* patch .altinstructions */
void *aseg = (void *)s->sh_addr;
apply_alternatives(aseg, aseg + s->sh_size);
}
}
}
jump_label_apply_nops(me);
return 0;
}