Commit 0c3b61e0 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Peter Zijlstra
Browse files

jump_label: s390: avoid pointless initial NOP patching 



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: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220615154142.1574619-2-ardb@kernel.org
parent a111daf0

arch/s390/include/asm/jump_label.h

+2 −3
Original line number Diff line number Diff line
@@ -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"

arch/s390/kernel/jump_label.c

+5 −18
Original line number Diff line number Diff line
@@ -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);

	}

	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();

}