Jump Label initialization

Jump Label initialization

[Jeremy Fitzhardinge]

Hi all,

I'm trying to use the jump label machinery as part of the pv ticketlock
work I'm doing on x86.

The problem I'm having at the moment is that I do my spinlock setup in
smp_prepare_boot_cpu(), which happens before jump_label_init() gets
called, and so the latter goes and nops out all my enabled jump label key.

I'm experimenting at the moment with a patch to allow
jump_label_enable() to be called fairly early, and have that be
respected by jump_label_init().  I'm doing this by replacing
arch_jump_label_poke_text_early() with
arch_jump_label_transform_early(), which shares most of its code with
its non-early variant, except that it expects to run in a pre-SMP
environment.

Does this seem plausible? (I haven't tested it yet.)

The x86, mips and sparc patches are fairly simple; I forgot to look at
powerpc, and I didn't fully investigate s390.

While my current use-case is x86-specific, it seems generally useful to
make the jump_label machinery available as early as possible. I wonder
if you have any suggestions about how to handle this?

Thanks,
    J

Re: Jump Label initialization

[David Miller]

From: Jeremy Fitzhardinge <jeremy@goop.org>
Date: Wed, 28 Sep 2011 19:14:52 -0700

> I'm experimenting at the moment with a patch to allow
> jump_label_enable() to be called fairly early, and have that be
> respected by jump_label_init().  I'm doing this by replacing
> arch_jump_label_poke_text_early() with
> arch_jump_label_transform_early(), which shares most of its code with
> its non-early variant, except that it expects to run in a pre-SMP
> environment.
> 
> Does this seem plausible? (I haven't tested it yet.)

I have no objections to this.

Re: Jump Label initialization

[Peter Zijlstra]

On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
> Hi all,
> 
> I'm trying to use the jump label machinery as part of the pv ticketlock
> work I'm doing on x86.
> 
> The problem I'm having at the moment is that I do my spinlock setup in
> smp_prepare_boot_cpu(), which happens before jump_label_init() gets
> called, and so the latter goes and nops out all my enabled jump label key.
> 
> I'm experimenting at the moment with a patch to allow
> jump_label_enable() to be called fairly early, and have that be
> respected by jump_label_init().  I'm doing this by replacing
> arch_jump_label_poke_text_early() with
> arch_jump_label_transform_early(), which shares most of its code with
> its non-early variant, except that it expects to run in a pre-SMP
> environment.
> 
> Does this seem plausible? (I haven't tested it yet.)
> 
> The x86, mips and sparc patches are fairly simple; I forgot to look at
> powerpc, and I didn't fully investigate s390.
> 
> While my current use-case is x86-specific, it seems generally useful to
> make the jump_label machinery available as early as possible. I wonder
> if you have any suggestions about how to handle this?

I also remember talking to Jason about a way to initialize a jump label
enabled, instead of the default disabled.

So yeah, I think your stuff would be useful..

Re: Jump Label initialization

[Jan Glauber]

On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
> Hi all,
> 
> I'm trying to use the jump label machinery as part of the pv ticketlock
> work I'm doing on x86.
> 
> The problem I'm having at the moment is that I do my spinlock setup in
> smp_prepare_boot_cpu(), which happens before jump_label_init() gets
> called, and so the latter goes and nops out all my enabled jump label key.
> 
> I'm experimenting at the moment with a patch to allow
> jump_label_enable() to be called fairly early, and have that be
> respected by jump_label_init().  I'm doing this by replacing
> arch_jump_label_poke_text_early() with
> arch_jump_label_transform_early(), which shares most of its code with
> its non-early variant, except that it expects to run in a pre-SMP
> environment.
> 
> Does this seem plausible? (I haven't tested it yet.)
> 
> The x86, mips and sparc patches are fairly simple; I forgot to look at
> powerpc, and I didn't fully investigate s390.

s390 does not have the early() variant since it didn't need it. On
pre-SMP we probably don't need stop_machine() so creating
arch_jump_label_transform_early() by leaving out stop_machine()
and patching the code directly should be fine.

Re: Jump Label initialization

[Steven Rostedt]

On Thu, 2011-09-29 at 14:04 +0200, Jan Glauber wrote:
> On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
> > Hi all,
> > 
> > I'm trying to use the jump label machinery as part of the pv ticketlock
> > work I'm doing on x86.
> > 
> > The problem I'm having at the moment is that I do my spinlock setup in
> > smp_prepare_boot_cpu(), which happens before jump_label_init() gets
> > called, and so the latter goes and nops out all my enabled jump label key.
> > 
> > I'm experimenting at the moment with a patch to allow
> > jump_label_enable() to be called fairly early, and have that be
> > respected by jump_label_init().  I'm doing this by replacing
> > arch_jump_label_poke_text_early() with
> > arch_jump_label_transform_early(), which shares most of its code with
> > its non-early variant, except that it expects to run in a pre-SMP
> > environment.
> > 
> > Does this seem plausible? (I haven't tested it yet.)
> > 
> > The x86, mips and sparc patches are fairly simple; I forgot to look at
> > powerpc, and I didn't fully investigate s390.
> 
> s390 does not have the early() variant since it didn't need it. On
> pre-SMP we probably don't need stop_machine() so creating
> arch_jump_label_transform_early() by leaving out stop_machine()
> and patching the code directly should be fine.

Also note that stop_machine() may only be needed by a few archs (maybe
only x86).

x86 has a nasty condition if you change code that is being loaded in
another CPUs pipeline, it could cause a GPF. I've been playing with this
on PPC and this does not have that same bug. In fact Benjamin told me
that PPC is fine with modifying instructions on a running system.

I plan on removing the stop_machine() from ftrace for those boxes. I
already have patches made, just need to spiffy them up a bit.

-- Steve

Re: Jump Label initialization

[Jan Glauber]

On Thu, 2011-09-29 at 08:40 -0400, Steven Rostedt wrote:
> On Thu, 2011-09-29 at 14:04 +0200, Jan Glauber wrote:
> > On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
> > > Hi all,
> > > 
> > > I'm trying to use the jump label machinery as part of the pv ticketlock
> > > work I'm doing on x86.
> > > 
> > > The problem I'm having at the moment is that I do my spinlock setup in
> > > smp_prepare_boot_cpu(), which happens before jump_label_init() gets
> > > called, and so the latter goes and nops out all my enabled jump label key.
> > > 
> > > I'm experimenting at the moment with a patch to allow
> > > jump_label_enable() to be called fairly early, and have that be
> > > respected by jump_label_init().  I'm doing this by replacing
> > > arch_jump_label_poke_text_early() with
> > > arch_jump_label_transform_early(), which shares most of its code with
> > > its non-early variant, except that it expects to run in a pre-SMP
> > > environment.
> > > 
> > > Does this seem plausible? (I haven't tested it yet.)
> > > 
> > > The x86, mips and sparc patches are fairly simple; I forgot to look at
> > > powerpc, and I didn't fully investigate s390.
> > 
> > s390 does not have the early() variant since it didn't need it. On
> > pre-SMP we probably don't need stop_machine() so creating
> > arch_jump_label_transform_early() by leaving out stop_machine()
> > and patching the code directly should be fine.
> 
> Also note that stop_machine() may only be needed by a few archs (maybe
> only x86).

s390 needs stop_machine() too. Instructions may be fetched multiple
times for a single execution and may also be fetched piecemeal.

--Jan

Re: Jump Label initialization

[Jeremy Fitzhardinge]

On 09/29/2011 05:04 AM, Jan Glauber wrote:
>
> s390 does not have the early() variant since it didn't need it. On
> pre-SMP we probably don't need stop_machine() so creating
> arch_jump_label_transform_early() by leaving out stop_machine()
> and patching the code directly should be fine.

Well, it occurs to me that if you're using jump_label_enable() very
early, then it will be using the full arch_jump_label_transform()
anyway.  While the stop_machine(), locking, etc that the full version
does is redundant in a pre-SMP environment, it shouldn't hurt, so
perhaps there's no need for an _early variant at all.

    J

Re: Jump Label initialization

[David Daney]

On 09/29/2011 09:45 AM, Jeremy Fitzhardinge wrote:
> On 09/29/2011 05:04 AM, Jan Glauber wrote:
>>
>> s390 does not have the early() variant since it didn't need it. On
>> pre-SMP we probably don't need stop_machine() so creating
>> arch_jump_label_transform_early() by leaving out stop_machine()
>> and patching the code directly should be fine.
>
> Well, it occurs to me that if you're using jump_label_enable() very
> early, then it will be using the full arch_jump_label_transform()
> anyway.  While the stop_machine(), locking, etc that the full version
> does is redundant in a pre-SMP environment, it shouldn't hurt, so
> perhaps there's no need for an _early variant at all.
>

You need a way to guarantee that the code you are modifying is not in 
the instruction cache of the off-line CPUs.

On our (Cavium) SMP MIPS systems, these off-line CPUs are most likely 
spinning in architecture specific smp startup code somewhere in the 
kernel image.  If this code happened to be adjacent to something the 
arch_jump_label_transform_early() would touch, we could have a problem.

The solution is fairly simple, just invalidate the instruction cache 
immediately upon leaving the spinning loop.

David Daney

Re: Jump Label initialization

[Jeremy Fitzhardinge]

On 09/29/2011 12:37 AM, Peter Zijlstra wrote:
> On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
>> Hi all,
>>
>> I'm trying to use the jump label machinery as part of the pv ticketlock
>> work I'm doing on x86.
>>
>> The problem I'm having at the moment is that I do my spinlock setup in
>> smp_prepare_boot_cpu(), which happens before jump_label_init() gets
>> called, and so the latter goes and nops out all my enabled jump label key.
>>
>> I'm experimenting at the moment with a patch to allow
>> jump_label_enable() to be called fairly early, and have that be
>> respected by jump_label_init().  I'm doing this by replacing
>> arch_jump_label_poke_text_early() with
>> arch_jump_label_transform_early(), which shares most of its code with
>> its non-early variant, except that it expects to run in a pre-SMP
>> environment.
>>
>> Does this seem plausible? (I haven't tested it yet.)
>>
>> The x86, mips and sparc patches are fairly simple; I forgot to look at
>> powerpc, and I didn't fully investigate s390.
>>
>> While my current use-case is x86-specific, it seems generally useful to
>> make the jump_label machinery available as early as possible. I wonder
>> if you have any suggestions about how to handle this?
> I also remember talking to Jason about a way to initialize a jump label
> enabled, instead of the default disabled.
>
> So yeah, I think your stuff would be useful..
>

Here's what I have, which appears to work on x86.  The non-x86
architecture changes are completely untested.

But I still question whether the _early variant is necessary at all.  If
it were, then jump_label_enable() should use when called early as well.

    J

diff --git a/arch/mips/kernel/jump_label.c b/arch/mips/kernel/jump_label.c
index 6001610..ddc9a65 100644
--- a/arch/mips/kernel/jump_label.c
+++ b/arch/mips/kernel/jump_label.c
@@ -20,8 +20,8 @@
 
 #define J_RANGE_MASK ((1ul << 28) - 1)
 
-void arch_jump_label_transform(struct jump_entry *e,
-			       enum jump_label_type type)
+static void __jump_label_transform(struct jump_entry *e,
+				   enum jump_label_type type)
 {
 	union mips_instruction insn;
 	union mips_instruction *insn_p =
@@ -40,15 +40,28 @@ void arch_jump_label_transform(struct jump_entry *e,
 		insn.word = 0; /* nop */
 	}
 
-	get_online_cpus();
-	mutex_lock(&text_mutex);
 	*insn_p = insn;
 
 	flush_icache_range((unsigned long)insn_p,
 			   (unsigned long)insn_p + sizeof(*insn_p));
+}
+
+void arch_jump_label_transform(struct jump_entry *e,
+			       enum jump_label_type type)
+{
+	get_online_cpus();
+	mutex_lock(&text_mutex);
+
+	__jump_label_tranform(e, type);
 
 	mutex_unlock(&text_mutex);
 	put_online_cpus();
 }
 
+void __init arch_jump_label_transform_early(struct jump_entry *e,
+					    enum jump_label_type type)
+{
+	__jump_label_tranform(e, type);
+}
+
 #endif /* HAVE_JUMP_LABEL */
diff --git a/arch/powerpc/kernel/jump_label.c b/arch/powerpc/kernel/jump_label.c
index 368d158..20c82fb 100644
--- a/arch/powerpc/kernel/jump_label.c
+++ b/arch/powerpc/kernel/jump_label.c
@@ -21,3 +21,9 @@ void arch_jump_label_transform(struct jump_entry *entry,
 	else
 		patch_instruction(addr, PPC_INST_NOP);
 }
+
+void __init arch_jump_label_transform_early(struct jump_entry *entry,
+					    enum jump_label_type type)
+{
+	arch_jump_label_transform(entry, type);
+}
diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
index 44cc06b..6001228 100644
--- a/arch/s390/kernel/jump_label.c
+++ b/arch/s390/kernel/jump_label.c
@@ -18,23 +18,12 @@ struct insn {
 } __packed;
 
 struct insn_args {
-	unsigned long *target;
-	struct insn *insn;
-	ssize_t size;
+	struct jump_entry *entry;
+	enum jump_label_type type;
 };
 
-static int __arch_jump_label_transform(void *data)
-{
-	struct insn_args *args = data;
-	int rc;
-
-	rc = probe_kernel_write(args->target, args->insn, args->size);
-	WARN_ON_ONCE(rc < 0);
-	return 0;
-}
-
-void arch_jump_label_transform(struct jump_entry *entry,
-			       enum jump_label_type type)
+static void __jump_label_transform(struct jump_entry *entry,
+				   enum jump_label_type type)
 {
 	struct insn_args args;
 	struct insn insn;
@@ -49,11 +38,33 @@ void arch_jump_label_transform(struct jump_entry *entry,
 		insn.offset = 0;
 	}
 
-	args.target = (void *) entry->code;
-	args.insn = &insn;
-	args.size = JUMP_LABEL_NOP_SIZE;
+	rc = probe_kernel_write(entry->code, &insn, JUMP_LABEL_NOP_SIZE);
+	WARN_ON_ONCE(rc < 0);
+}
+
+static int __sm_arch_jump_label_transform(void *data)
+{
+	struct insn_args *args = data;
+
+	__jump_label_transform(args->entry, args->type);
+	return 0;
+}
 
-	stop_machine(__arch_jump_label_transform, &args, NULL);
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	struct insn_args args;
+
+	args.entry = entry;
+	args.type = type;
+
+	stop_machine(__sm_arch_jump_label_transform, &args, NULL);
+}
+
+void __init arch_jump_label_transform_early(struct jump_entry *entry,
+					    enum jump_label_type type)
+{
+	__jump_label_transform(entry, type);
 }
 
 #endif
diff --git a/arch/sparc/kernel/jump_label.c b/arch/sparc/kernel/jump_label.c
index ea2dafc..d3dad25 100644
--- a/arch/sparc/kernel/jump_label.c
+++ b/arch/sparc/kernel/jump_label.c
@@ -8,8 +8,8 @@
 
 #ifdef HAVE_JUMP_LABEL
 
-void arch_jump_label_transform(struct jump_entry *entry,
-			       enum jump_label_type type)
+static void __jump_label_transform(struct jump_entry *entry,
+				   enum jump_label_type type)
 {
 	u32 val;
 	u32 *insn = (u32 *) (unsigned long) entry->code;
@@ -28,20 +28,26 @@ void arch_jump_label_transform(struct jump_entry *entry,
 		val = 0x01000000;
 	}
 
-	get_online_cpus();
-	mutex_lock(&text_mutex);
 	*insn = val;
 	flushi(insn);
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	get_online_cpus();
+	mutex_lock(&text_mutex);
+
+	__jump_label_transform(entry, type);
+
 	mutex_unlock(&text_mutex);
 	put_online_cpus();
 }
 
-void arch_jump_label_text_poke_early(jump_label_t addr)
+void __init arch_jump_label_transform_early(struct jump_entry *entry,
+					    enum jump_label_type type)
 {
-	u32 *insn_p = (u32 *) (unsigned long) addr;
-
-	*insn_p = 0x01000000;
-	flushi(insn_p);
+	__jump_label_transform(entry, type);
 }
 
 #endif
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 3fee346..0887b59 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -24,8 +24,9 @@ union jump_code_union {
 	} __attribute__((packed));
 };
 
-void arch_jump_label_transform(struct jump_entry *entry,
-			       enum jump_label_type type)
+static void __jump_label_transform(struct jump_entry *entry,
+				   enum jump_label_type type,
+				   void *(*poker)(void *, const void *, size_t))
 {
 	union jump_code_union code;
 
@@ -35,17 +36,24 @@ void arch_jump_label_transform(struct jump_entry *entry,
 				(entry->code + JUMP_LABEL_NOP_SIZE);
 	} else
 		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+
+	(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
 	get_online_cpus();
 	mutex_lock(&text_mutex);
-	text_poke_smp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+	__jump_label_transform(entry, type, text_poke_smp);
 	mutex_unlock(&text_mutex);
 	put_online_cpus();
 }
 
-void arch_jump_label_text_poke_early(jump_label_t addr)
+void __init arch_jump_label_transform_early(struct jump_entry *entry,
+					    enum jump_label_type type)
 {
-	text_poke_early((void *)addr, ideal_nops[NOP_ATOMIC5],
-			JUMP_LABEL_NOP_SIZE);
+	__jump_label_transform(entry, type, text_poke_early);
 }
 
 #endif
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 66f23dc..c8fb1b3 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -28,9 +28,9 @@ struct module;
 #ifdef HAVE_JUMP_LABEL
 
 #ifdef CONFIG_MODULES
-#define JUMP_LABEL_INIT {{ 0 }, NULL, NULL}
+#define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL, NULL}
 #else
-#define JUMP_LABEL_INIT {{ 0 }, NULL}
+#define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL}
 #endif
 
 static __always_inline bool static_branch(struct jump_label_key *key)
@@ -45,7 +45,8 @@ extern void jump_label_lock(void);
 extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
 				 enum jump_label_type type);
-extern void arch_jump_label_text_poke_early(jump_label_t addr);
+extern void arch_jump_label_transform_early(struct jump_entry *entry,
+				 enum jump_label_type type);
 extern int jump_label_text_reserved(void *start, void *end);
 extern void jump_label_inc(struct jump_label_key *key);
 extern void jump_label_dec(struct jump_label_key *key);
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index a8ce450..3010bcf 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -121,13 +121,6 @@ static void __jump_label_update(struct jump_label_key *key,
 	}
 }
 
-/*
- * Not all archs need this.
- */
-void __weak arch_jump_label_text_poke_early(jump_label_t addr)
-{
-}
-
 static __init int jump_label_init(void)
 {
 	struct jump_entry *iter_start = __start___jump_table;
@@ -139,12 +132,15 @@ static __init int jump_label_init(void)
 	jump_label_sort_entries(iter_start, iter_stop);
 
 	for (iter = iter_start; iter < iter_stop; iter++) {
-		arch_jump_label_text_poke_early(iter->code);
-		if (iter->key == (jump_label_t)(unsigned long)key)
+		struct jump_label_key *iterk;
+
+		iterk = (struct jump_label_key *)(unsigned long)iter->key;
+		arch_jump_label_transform_early(iter, jump_label_enabled(iterk) ?
+						JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+		if (iterk == key)
 			continue;
 
-		key = (struct jump_label_key *)(unsigned long)iter->key;
-		atomic_set(&key->enabled, 0);
+		key = iterk;
 		key->entries = iter;
 #ifdef CONFIG_MODULES
 		key->next = NULL;
@@ -212,7 +208,7 @@ void jump_label_apply_nops(struct module *mod)
 		return;
 
 	for (iter = iter_start; iter < iter_stop; iter++)
-		arch_jump_label_text_poke_early(iter->code);
+		arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
 }
 
 static int jump_label_add_module(struct module *mod)

	J

Re: Jump Label initialization

[Steven Rostedt]

On Thu, 2011-09-29 at 15:20 -0700, Jeremy Fitzhardinge wrote:
> +static void __jump_label_transform(struct jump_entry *entry,
> +                                  enum jump_label_type type,
> +                                  void *(*poker)(void *, const void *, size_t))
>  { 

Jump labels have taken up gambling?


-- Steve