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Message-Id: <20191007090012.11817198.6@infradead.org>
Date: Mon, 07 Oct 2019 10:44:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: peterz@...radead.org, linux-kernel@...r.kernel.org,
rostedt@...dmis.org, mhiramat@...nel.org, bristot@...hat.com,
jbaron@...mai.com, torvalds@...ux-foundation.org,
tglx@...utronix.de, mingo@...nel.org, namit@...are.com,
hpa@...or.com, luto@...nel.org, ard.biesheuvel@...aro.org,
jpoimboe@...hat.com, hjl.tools@...il.com
Subject: [RFC][PATCH 6/9] jump_label, x86: Add variable length patching support
This allows the patching to to emit 2 byte JMP/NOP instruction in
addition to the 5 byte JMP/NOP we already did. This allows for more
compact code.
This code is not yet used, as we don't emit shorter code at compile
time yet.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/jump_label.h | 8 +++--
arch/x86/include/asm/nops.h | 1
arch/x86/kernel/jump_label.c | 60 ++++++++++++++++++++++++--------------
3 files changed, 45 insertions(+), 24 deletions(-)
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -5,9 +5,11 @@
#define HAVE_JUMP_LABEL_BATCH
#ifdef CONFIG_X86_64
-# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC
+# define STATIC_KEY_NOP2 P6_NOP2
+# define STATIC_KEY_NOP5 P6_NOP5_ATOMIC
#else
-# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
+# define STATIC_KEY_NOP2 GENERIC_NOP2
+# define STATIC_KEY_NOP5 GENERIC_NOP5_ATOMIC
#endif
#include <asm/asm.h>
@@ -29,7 +31,7 @@
static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
{
asm_volatile_goto("1:"
- ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
+ ".byte " __stringify(STATIC_KEY_NOP5) "\n\t"
JUMP_TABLE_ENTRY
: : "i" (key), "i" (branch) : : l_yes);
--- a/arch/x86/include/asm/nops.h
+++ b/arch/x86/include/asm/nops.h
@@ -5,6 +5,7 @@
/*
* Define nops for use with alternative() and for tracing.
*
+ * *_NOP2 must be a single instruction
* *_NOP5_ATOMIC must be a single instruction.
*/
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -21,50 +21,70 @@ int arch_jump_entry_size(struct jump_ent
return JMP32_INSN_SIZE;
}
-static const void *
-__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
+struct jump_label_patch {
+ const void *code;
+ int size;
+};
+
+static struct jump_label_patch
+__jump_label_patch(struct jump_entry *entry, enum jump_label_type type, int init)
{
- const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
- const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
- const void *expect, *code;
+ const unsigned char default_nop2[] = { STATIC_KEY_NOP2 };
+ const unsigned char default_nop5[] = { STATIC_KEY_NOP5 };
+ const void *expect, *code, *nop, *default_nop;
const void *addr, *dest;
- int line;
+ int line, size;
addr = (void *)jump_entry_code(entry);
dest = (void *)jump_entry_target(entry);
- code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest);
+ size = arch_jump_entry_size(entry);
+ switch (size) {
+ case JMP8_INSN_SIZE:
+ code = text_gen_insn(JMP8_INSN_OPCODE, addr, dest);
+ default_nop = default_nop2;
+ nop = ideal_nops[2];
+ break;
+
+ case JMP32_INSN_SIZE:
+ code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest);
+ default_nop = default_nop5;
+ nop = ideal_nops[NOP_ATOMIC5];
+ break;
+
+ default: BUG();
+ }
if (init) {
expect = default_nop; line = __LINE__;
} else if (type == JUMP_LABEL_JMP) {
- expect = ideal_nop; line = __LINE__;
+ expect = nop; line = __LINE__;
} else {
expect = code; line = __LINE__;
}
- if (memcmp(addr, expect, JUMP_LABEL_NOP_SIZE)) {
+ if (memcmp(addr, expect, size)) {
/*
* The location is not an op that we were expecting.
* Something went wrong. Crash the box, as something could be
* corrupting the kernel.
*/
- pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) line:%d init:%d type:%d\n",
- addr, addr, addr, expect, line, init, type);
+ pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) line:%d init:%d size:%d type:%d\n",
+ addr, addr, addr, expect, line, init, size, type);
BUG();
}
if (type == JUMP_LABEL_NOP)
- code = ideal_nop;
+ code = nop;
- return code;
+ return (struct jump_label_patch){.code = code, .size = size};
}
static void inline __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
int init)
{
- const void *opcode = __jump_label_set_jump_code(entry, type, init);
+ const struct jump_label_patch jlp = __jump_label_patch(entry, type, init);
/*
* As long as only a single processor is running and the code is still
@@ -78,12 +98,11 @@ static void inline __jump_label_transfor
* always nop being the 'currently valid' instruction
*/
if (init || system_state == SYSTEM_BOOTING) {
- text_poke_early((void *)jump_entry_code(entry), opcode,
- JUMP_LABEL_NOP_SIZE);
+ text_poke_early((void *)jump_entry_code(entry), jlp.code, jlp.size);
return;
}
- text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL);
+ text_poke_bp((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
}
static void __ref jump_label_transform(struct jump_entry *entry,
@@ -104,7 +123,7 @@ void arch_jump_label_transform(struct ju
bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type)
{
- const void *opcode;
+ struct jump_label_patch jlp;
if (system_state == SYSTEM_BOOTING) {
/*
@@ -115,9 +134,8 @@ bool arch_jump_label_transform_queue(str
}
mutex_lock(&text_mutex);
- opcode = __jump_label_set_jump_code(entry, type, 0);
- text_poke_queue((void *)jump_entry_code(entry),
- opcode, JUMP_LABEL_NOP_SIZE, NULL);
+ jlp = __jump_label_patch(entry, type, 0);
+ text_poke_queue((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
mutex_unlock(&text_mutex);
return true;
}
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