[PATCH V2 0/3] kprobe: Optimize the performance of patching ss

[PATCH V2 0/3] kprobe: Optimize the performance of patching ss

[Liao Chang]

Single-step slot would not be used until kprobe is enabled, that means
no race condition occurs on it under SMP, hence it is safe to pacth ss
slot without stopping machine.

v2:
Backport riscv patch to cksy and arm64.

Liao Chang (3):
  riscv/kprobe: Optimize the performance of patching single-step slot
  csky/kprobe: Optimize the performance of patching single-step slot
  arm64/kprobe: Optimize the performance of patching single-step slot

 arch/arm64/kernel/probes/kprobes.c | 5 ++---
 arch/csky/kernel/probes/kprobes.c  | 6 +++++-
 arch/riscv/kernel/probes/kprobes.c | 8 +++++---
 3 files changed, 12 insertions(+), 7 deletions(-)

-- 
2.17.1


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[PATCH V2 1/3] riscv/kprobe: Optimize the performance of patching single-step slot

[Liao Chang]

Single-step slot would not be used until kprobe is enabled, that means
no race condition occurs on it under SMP, hence it is safe to pacth ss
slot without stopping machine.

Signed-off-by: Liao Chang <liaochang1@huawei.com>
---
 arch/riscv/kernel/probes/kprobes.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index e6e950b7cf32..bc1f39b96e41 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -24,12 +24,14 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
 	unsigned long offset = GET_INSN_LENGTH(p->opcode);
+	kprobe_opcode_t slot[MAX_INSN_SIZE];
 
 	p->ainsn.api.restore = (unsigned long)p->addr + offset;
 
-	patch_text(p->ainsn.api.insn, p->opcode);
-	patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
-		   __BUG_INSN_32);
+	memcpy(slot, &p->opcode, offset);
+	*(kprobe_opcode_t *)((unsigned long)slot + offset) = __BUG_INSN_32;
+	patch_text_nosync(p->ainsn.api.insn, slot,
+			  offset + GET_INSN_LENGTH(__BUG_INSN_32));
 }
 
 static void __kprobes arch_prepare_simulate(struct kprobe *p)
-- 
2.17.1


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[PATCH V2 2/3] csky/kprobe: Optimize the performance of patching single-step slot

[Liao Chang]

Single-step slot would not be used until kprobe is enabled, that means
no race condition occurs on it under SMP, hence it is safe to pacth ss
slot without stopping machine.

Signed-off-by: Liao Chang <liaochang1@huawei.com>
---
 arch/csky/kernel/probes/kprobes.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/csky/kernel/probes/kprobes.c b/arch/csky/kernel/probes/kprobes.c
index 3c6e5c725d81..4feb5ce16264 100644
--- a/arch/csky/kernel/probes/kprobes.c
+++ b/arch/csky/kernel/probes/kprobes.c
@@ -57,7 +57,11 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 
 	p->ainsn.api.restore = (unsigned long)p->addr + offset;
 
-	patch_text(p->ainsn.api.insn, p->opcode);
+	memcpy(p->ainsn.api.insn, &p->opcode, offset);
+	dcache_wb_range((unsigned long)p->ainsn.api.insn,
+			(unsigned long)p->ainsn.api.insn + offset);
+	icache_inv_range((unsigned long)p->ainsn.api.insn,
+			 (unsigned long)p->ainsn.api.insn + offset);
 }
 
 static void __kprobes arch_prepare_simulate(struct kprobe *p)
-- 
2.17.1


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[PATCH V2 3/3] arm64/kprobe: Optimize the performance of patching single-step slot

[Liao Chang]

Single-step slot would not be used until kprobe is enabled, that means
no race condition occurs on it under SMP, hence it is safe to pacth ss
slot without stopping machine.

Signed-off-by: Liao Chang <liaochang1@huawei.com>
---
 arch/arm64/kernel/probes/kprobes.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d1d182320245..5902e33fd3b6 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -44,11 +44,10 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
 	kprobe_opcode_t *addr = p->ainsn.api.insn;
-	void *addrs[] = {addr, addr + 1};
-	u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS};
 
 	/* prepare insn slot */
-	aarch64_insn_patch_text(addrs, insns, 2);
+	aarch64_insn_write(addr, p->opcode);
+	aarch64_insn_write(addr + 1, BRK64_OPCODE_KPROBES_SS);
 
 	flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));
 
-- 
2.17.1


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Re: [PATCH V2 0/3] kprobe: Optimize the performance of patching ss

[Masami Hiramatsu]

On Tue, 13 Sep 2022 11:34:51 +0800
Liao Chang <liaochang1@huawei.com> wrote:

> Single-step slot would not be used until kprobe is enabled, that means
> no race condition occurs on it under SMP, hence it is safe to pacth ss
> slot without stopping machine.

All these patches look good to me, since single-step slot must not
be executed until it is prepared.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
for this series.

But I need Ack by each architecture maintainer.

Thank you,

> 
> v2:
> Backport riscv patch to cksy and arm64.
> 
> Liao Chang (3):
>   riscv/kprobe: Optimize the performance of patching single-step slot
>   csky/kprobe: Optimize the performance of patching single-step slot
>   arm64/kprobe: Optimize the performance of patching single-step slot
> 
>  arch/arm64/kernel/probes/kprobes.c | 5 ++---
>  arch/csky/kernel/probes/kprobes.c  | 6 +++++-
>  arch/riscv/kernel/probes/kprobes.c | 8 +++++---
>  3 files changed, 12 insertions(+), 7 deletions(-)
> 
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

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Re: [PATCH V2 3/3] arm64/kprobe: Optimize the performance of patching single-step slot

[Will Deacon]

On Tue, Sep 13, 2022 at 11:34:54AM +0800, Liao Chang wrote:
> Single-step slot would not be used until kprobe is enabled, that means
> no race condition occurs on it under SMP, hence it is safe to pacth ss
> slot without stopping machine.
> 
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
>  arch/arm64/kernel/probes/kprobes.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index d1d182320245..5902e33fd3b6 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -44,11 +44,10 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>  {
>  	kprobe_opcode_t *addr = p->ainsn.api.insn;
> -	void *addrs[] = {addr, addr + 1};
> -	u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS};
>  
>  	/* prepare insn slot */
> -	aarch64_insn_patch_text(addrs, insns, 2);
> +	aarch64_insn_write(addr, p->opcode);
> +	aarch64_insn_write(addr + 1, BRK64_OPCODE_KPROBES_SS);
>  
>  	flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));

Hmm, so it looks like prior to your change we were doing the cache
maintebnance twice: once in aarch64_insn_patch_text() from stop machine
context and then again in the flush_icache_range() call above.

I suppose the cleanest thing would be to drop the flush_icache_range()
call and then use aarch64_insn_patch_text_nosync() instead of
aarch64_insn_write() in your change.

Will

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Re: [PATCH V2 3/3] arm64/kprobe: Optimize the performance of patching single-step slot

[liaochang (A)]

在 2022/9/22 21:38, Will Deacon 写道:
> On Tue, Sep 13, 2022 at 11:34:54AM +0800, Liao Chang wrote:
>> Single-step slot would not be used until kprobe is enabled, that means
>> no race condition occurs on it under SMP, hence it is safe to pacth ss
>> slot without stopping machine.
>>
>> Signed-off-by: Liao Chang <liaochang1@huawei.com>
>> ---
>>  arch/arm64/kernel/probes/kprobes.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index d1d182320245..5902e33fd3b6 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -44,11 +44,10 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>>  {
>>  	kprobe_opcode_t *addr = p->ainsn.api.insn;
>> -	void *addrs[] = {addr, addr + 1};
>> -	u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS};
>>  
>>  	/* prepare insn slot */
>> -	aarch64_insn_patch_text(addrs, insns, 2);
>> +	aarch64_insn_write(addr, p->opcode);
>> +	aarch64_insn_write(addr + 1, BRK64_OPCODE_KPROBES_SS);
>>  
>>  	flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));
> 
> Hmm, so it looks like prior to your change we were doing the cache
> maintebnance twice: once in aarch64_insn_patch_text() from stop machine
> context and then again in the flush_icache_range() call above.
> 
> I suppose the cleanest thing would be to drop the flush_icache_range()
> call and then use aarch64_insn_patch_text_nosync() instead of
> aarch64_insn_write() in your change.

OK，I will improve it in next version, thanks.

> 
> Will
> .

-- 
BR,
Liao, Chang

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