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jump_label: s390: avoid pointless initial NOP patching

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Patching NOPs into other NOPs at boot time serves no purpose, so let's
use the same NOP encodings at compile time and runtime.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220615154142.1574619-2-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2022-06-15 17:41:40 +02:00 committed by Peter Zijlstra
parent a111daf0c5
commit 0c3b61e00a
2 changed files with 7 additions and 21 deletions
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5
arch/s390/include/asm/jump_label.h
View File

@ -10,7 +10,6 @@
#include <linux/stringify.h>
#define JUMP_LABEL_NOP_SIZE 6
#define JUMP_LABEL_NOP_OFFSET 2
#ifdef CONFIG_CC_IS_CLANG
#define JUMP_LABEL_STATIC_KEY_CONSTRAINT "i"
@ -21,12 +20,12 @@
#endif
/*
* We use a brcl 0,2 instruction for jump labels at compile time so it
* We use a brcl 0,<offset> instruction for jump labels so it
* can be easily distinguished from a hotpatch generated instruction.
*/
static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
{
asm_volatile_goto("0: brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
asm_volatile_goto("0: brcl 0,%l[label]\n"
".pushsection __jump_table,\"aw\"\n"
".balign 8\n"
".long 0b-.,%l[label]-.\n"

23
arch/s390/kernel/jump_label.c
View File

@ -44,14 +44,8 @@ static void jump_label_bug(struct jump_entry *entry, struct insn *expected,
panic("Corrupted kernel text");
}
static struct insn orignop = {
.opcode = 0xc004,
.offset = JUMP_LABEL_NOP_OFFSET >> 1,
};
static void jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
int init)
enum jump_label_type type)
{
void *code = (void *)jump_entry_code(entry);
struct insn old, new;
@ -63,27 +57,22 @@ static void jump_label_transform(struct jump_entry *entry,
jump_label_make_branch(entry, &old);
jump_label_make_nop(entry, &new);
}
if (init) {
if (memcmp(code, &orignop, sizeof(orignop)))
jump_label_bug(entry, &orignop, &new);
} else {
if (memcmp(code, &old, sizeof(old)))
jump_label_bug(entry, &old, &new);
}
if (memcmp(code, &old, sizeof(old)))
jump_label_bug(entry, &old, &new);
s390_kernel_write(code, &new, sizeof(new));
}
void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type)
{
jump_label_transform(entry, type, 0);
jump_label_transform(entry, type);
text_poke_sync();
}
bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type)
{
jump_label_transform(entry, type, 0);
jump_label_transform(entry, type);
return true;
}
@ -95,6 +84,4 @@ void arch_jump_label_transform_apply(void)
void __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
enum jump_label_type type)
{
jump_label_transform(entry, type, 1);
text_poke_sync();
}