Message-Id: <20211214092657.5b9c26b4e3852602eced4fda@kernel.org>
Date:   Tue, 14 Dec 2021 09:26:57 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     Qi Liu <liuqi115@...wei.com>, catalin.marinas@....com,
        mhiramat@...nel.org, linux-arm-kernel@...ts.infradead.org,
        song.bao.hua@...ilicon.com, prime.zeng@...ilicon.com,
        robin.murphy@....com, linuxarm@...wei.com,
        linux-kernel@...r.kernel.org, jianhua.ljh@...il.com
Subject: Re: [PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64

On Mon, 13 Dec 2021 18:38:52 +0000
Will Deacon <will@...nel.org> wrote:

> Hi,
> 
> [+Janet Liu]
> 
> On Tue, Dec 07, 2021 at 08:40:02PM +0800, Qi Liu wrote:
> > This patch introduce optprobe for ARM64. In optprobe, probed
> > instruction is replaced by a branch instruction to trampoline.
> > 
> > Performance of optprobe on Hip08 platform is test using kprobe
> > example module[1] to analyze the latency of a kernel function,
> > and here is the result:
> > 
> > common kprobe:
> > [280709.846380] do_empty returned 0 and took 1530 ns to execute
> > [280709.852057] do_empty returned 0 and took 550 ns to execute
> > [280709.857631] do_empty returned 0 and took 440 ns to execute
> > [280709.863215] do_empty returned 0 and took 380 ns to execute
> > [280709.868787] do_empty returned 0 and took 360 ns to execute
> > [280709.874362] do_empty returned 0 and took 340 ns to execute
> > [280709.879936] do_empty returned 0 and took 320 ns to execute
> > [280709.885505] do_empty returned 0 and took 300 ns to execute
> > [280709.891075] do_empty returned 0 and took 280 ns to execute
> > [280709.896646] do_empty returned 0 and took 290 ns to execute
> > 
> > optprobe:
> > [ 2965.964572] do_empty returned 0 and took 90 ns to execute
> > [ 2965.969952] do_empty returned 0 and took 80 ns to execute
> > [ 2965.975332] do_empty returned 0 and took 70 ns to execute
> > [ 2965.980714] do_empty returned 0 and took 60 ns to execute
> > [ 2965.986128] do_empty returned 0 and took 80 ns to execute
> > [ 2965.991507] do_empty returned 0 and took 70 ns to execute
> > [ 2965.996884] do_empty returned 0 and took 70 ns to execute
> > [ 2966.002262] do_empty returned 0 and took 80 ns to execute
> > [ 2966.007642] do_empty returned 0 and took 70 ns to execute
> > [ 2966.013020] do_empty returned 0 and took 70 ns to execute
> > [ 2966.018400] do_empty returned 0 and took 70 ns to execute
> > 
> > As the result shows, optprobe can greatly reduce the latency. Big
> > latency of common kprobe will significantly impact the real result
> > while doing performance analysis or debugging performance issues
> > in lab, so optprobe is useful in this scenario.
> > 
> > Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> > Signed-off-by: Qi Liu <liuqi115@...wei.com>
> > 
> > Note:
> > As branch instruction in Arm64 has a 128M range limitation, optprobe
> > could only used when offset between probe point and trampoline
> > is less than 128M, otherwise kernel will choose common kprobe
> > automaticly.
> > 
> > Limitation caused by branch isn't unique to Arm64, but also to
> > x86/arm/powerpc.
> > 
> > In fact, Module PLT has been tried to get rid of limiation, but
> > destination of PLT must be a fixed value, and we need to modify
> > the destination (as each optprobe has its own trampoline).
> > 
> > As discussed with Masami[2], we can start with core-kernel point
> > (within 128M) as the first step, like other architectures.
> > 
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kprobes/kretprobe_example.c
> > [2] https://lore.kernel.org/lkml/20211201105001.5164f98ba783e7207df1229c@kernel.org/
> > ---
> >  arch/arm64/Kconfig                            |   1 +
> >  arch/arm64/include/asm/kprobes.h              |  21 ++
> >  arch/arm64/kernel/probes/Makefile             |   2 +
> >  arch/arm64/kernel/probes/opt_arm64.c          | 199 ++++++++++++++++++
> >  .../arm64/kernel/probes/optprobe_trampoline.S |  97 +++++++++
> >  include/linux/kprobes.h                       |   2 +
> >  kernel/kprobes.c                              |  22 ++
> >  7 files changed, 344 insertions(+)
> >  create mode 100644 arch/arm64/kernel/probes/opt_arm64.c
> >  create mode 100644 arch/arm64/kernel/probes/optprobe_trampoline.S
> 
> I've not looked at these changes in detail, but it looks like there is an
> independent patch from Janet Liu trying to do the same thing:
> 
> https://lore.kernel.org/r/1635858706-27320-1-git-send-email-jianhua.ljh@gmail.com
> 

Thanks for noticing. I missed it.

> The patch here from Qi Liu looks like it's a bit further along, but it
> would be good for Janet to at least test it out and confirm that it works
> for them.

Yeah, it's now v5.
But it seems Janet's one also has good points. I would like Janet's sharing
save_all_base_regs macro and the comment about the branch instruction.

> 
> Cheers,
> 
> Will
> 
> [Kept diff inline for Janet]

Janet, please feel free to review and test it. It is important that you confirm
this can work with your envionment too.
I will review your KPROBE_ON_FTRACE patch. 

Thank you,

> 
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index c4207cf9bb17..6b68ec498e67 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -200,6 +200,7 @@ config ARM64
> >  	select HAVE_STACKPROTECTOR
> >  	select HAVE_SYSCALL_TRACEPOINTS
> >  	select HAVE_KPROBES
> > +	select HAVE_OPTPROBES
> >  	select HAVE_KRETPROBES
> >  	select HAVE_GENERIC_VDSO
> >  	select IOMMU_DMA if IOMMU_SUPPORT
> > diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> > index 05cd82eeca13..3838e4317877 100644
> > --- a/arch/arm64/include/asm/kprobes.h
> > +++ b/arch/arm64/include/asm/kprobes.h
> > @@ -39,6 +39,27 @@ void arch_remove_kprobe(struct kprobe *);
> >  int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
> >  int kprobe_exceptions_notify(struct notifier_block *self,
> >  			     unsigned long val, void *data);
> > +
> > +struct arch_optimized_insn {
> > +	kprobe_opcode_t orig_insn[1];
> > +	kprobe_opcode_t *trampoline;
> > +};
> > +
> > +#define MAX_OPTIMIZED_LENGTH	sizeof(kprobe_opcode_t)
> > +#define MAX_OPTINSN_SIZE                                                       \
> > +	((unsigned long)optprobe_template_restore_end - (unsigned long)optprobe_template_entry)
> > +
> > +extern __visible kprobe_opcode_t optprobe_template_entry[];
> > +extern __visible kprobe_opcode_t optprobe_template_val[];
> > +extern __visible kprobe_opcode_t optprobe_template_common[];
> > +extern __visible kprobe_opcode_t optprobe_template_end[];
> > +extern __visible kprobe_opcode_t optprobe_template_restore_begin[];
> > +extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn[];
> > +extern __visible kprobe_opcode_t optprobe_template_restore_end[];
> > +extern __visible kprobe_opcode_t optinsn_slot[];
> > +
> > +void optprobe_common(void);
> > +
> >  void __kretprobe_trampoline(void);
> >  void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
> >  
> > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
> > index 8e4be92e25b1..07105fd3261d 100644
> > --- a/arch/arm64/kernel/probes/Makefile
> > +++ b/arch/arm64/kernel/probes/Makefile
> > @@ -4,3 +4,5 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o	\
> >  				   simulate-insn.o
> >  obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o	\
> >  				   simulate-insn.o
> > +obj-$(CONFIG_OPTPROBES)		+= opt_arm64.o			\
> > +				   optprobe_trampoline.o
> > diff --git a/arch/arm64/kernel/probes/opt_arm64.c b/arch/arm64/kernel/probes/opt_arm64.c
> > new file mode 100644
> > index 000000000000..1bad5cddcdf2
> > --- /dev/null
> > +++ b/arch/arm64/kernel/probes/opt_arm64.c
> > @@ -0,0 +1,199 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Code for Kernel probes Jump optimization.
> > + *
> > + * Copyright (C) 2021 Hisilicon Limited
> > + */
> > +
> > +#include <linux/jump_label.h>
> > +#include <linux/kprobes.h>
> > +
> > +#include <asm/cacheflush.h>
> > +#include <asm/compiler.h>
> > +#include <asm/insn.h>
> > +#include <asm/kprobes.h>
> > +#include <asm/patching.h>
> > +
> > +#define OPTPROBE_BATCH_SIZE 64
> > +#define GET_LO_VAL(val)		FIELD_GET(GENMASK(31, 0), val)
> > +#define GET_HI_VAL(val)		FIELD_GET(GENMASK(63, 32), val)
> > +
> > +#define TMPL_VAL_IDX \
> > +	(optprobe_template_val - optprobe_template_entry)
> > +#define TMPL_CALL_COMMON \
> > +	(optprobe_template_common - optprobe_template_entry)
> > +#define TMPL_RESTORE_ORIGN_INSN \
> > +	(optprobe_template_restore_orig_insn - optprobe_template_entry)
> > +#define TMPL_RESTORE_END \
> > +	(optprobe_template_restore_end - optprobe_template_entry)
> > +#define TMPL_END_IDX \
> > +	(optprobe_template_end - optprobe_template_entry)
> > +
> > +static bool insn_page_in_use;
> > +
> > +void *alloc_optinsn_page(void)
> > +{
> > +	if (insn_page_in_use)
> > +		return NULL;
> > +	insn_page_in_use = true;
> > +	return &optinsn_slot;
> > +}
> > +
> > +void free_optinsn_page(void *page)
> > +{
> > +	insn_page_in_use = false;
> > +}
> > +
> > +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
> > +{
> > +	return 0;
> > +}
> > +
> > +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
> > +{
> > +	return optinsn->trampoline != NULL;
> > +}
> > +
> > +int arch_within_optimized_kprobe(struct optimized_kprobe *op, kprobe_opcode_t *addr)
> > +{
> > +	return op->kp.addr == addr;
> > +}
> > +
> > +static void optprobe_set_pc_value(struct optimized_kprobe *op, struct pt_regs *regs)
> > +{
> > +	regs->pc = (unsigned long)op->kp.addr;
> > +}
> > +
> > +static int optprobe_check_branch_limit(unsigned long pc, unsigned long addr)
> > +{
> > +	long offset;
> > +
> > +	if ((pc & 0x3) || (addr & 0x3))
> > +		return -ERANGE;
> > +
> > +	offset = (long)addr - (long)pc;
> > +	if (offset < -SZ_128M || offset >= SZ_128M)
> > +		return -ERANGE;
> > +
> > +	return 0;
> > +}
> > +
> > +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
> > +{
> > +	kprobe_opcode_t *code, *buf;
> > +	u32 insn;
> > +	int ret = -ENOMEM;
> > +	int i;
> > +
> > +	buf = kcalloc(MAX_OPTINSN_SIZE, sizeof(kprobe_opcode_t), GFP_KERNEL);
> > +	if (!buf)
> > +		return ret;
> > +
> > +	code = get_optinsn_slot();
> > +	if (!code)
> > +		goto out;
> > +
> > +	if (optprobe_check_branch_limit((unsigned long)code, (unsigned long)orig->addr + 8)) {
> > +		ret = -ERANGE;
> > +		goto error;
> > +	}
> > +
> > +	op->set_pc = optprobe_set_pc_value;
> > +	memcpy(buf, optprobe_template_entry, MAX_OPTINSN_SIZE * sizeof(kprobe_opcode_t));
> > +
> > +	insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_CALL_COMMON],
> > +					   (unsigned long)&optprobe_common,
> > +					   AARCH64_INSN_BRANCH_LINK);
> > +	buf[TMPL_CALL_COMMON] = insn;
> > +
> > +	insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_RESTORE_END],
> > +					   (unsigned long)op->kp.addr + 4,
> > +					   AARCH64_INSN_BRANCH_NOLINK);
> > +	buf[TMPL_RESTORE_END] = insn;
> > +
> > +	buf[TMPL_VAL_IDX] = cpu_to_le32(GET_LO_VAL((unsigned long)op));
> > +	buf[TMPL_VAL_IDX + 1] = cpu_to_le32(GET_HI_VAL((unsigned long)op));
> > +	buf[TMPL_RESTORE_ORIGN_INSN] = orig->opcode;
> > +
> > +	/* Setup template */
> > +	for (i = 0; i < MAX_OPTINSN_SIZE; i++)
> > +		aarch64_insn_patch_text_nosync(code + i, buf[i]);
> > +
> > +	flush_icache_range((unsigned long)code, (unsigned long)(&code[TMPL_VAL_IDX]));
> > +	/* Set op->optinsn.trampoline means prepared. */
> > +	op->optinsn.trampoline = code;
> > +
> > +out:
> > +	kfree(buf);
> > +	return ret;
> > +
> > +error:
> > +	free_optinsn_slot(code, 0);
> > +	goto out;
> > +}
> > +
> > +void arch_optimize_kprobes(struct list_head *oplist)
> > +{
> > +	struct optimized_kprobe *op, *tmp;
> > +	kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE];
> > +	void *addrs[OPTPROBE_BATCH_SIZE];
> > +	int i = 0;
> > +
> > +	list_for_each_entry_safe(op, tmp, oplist, list) {
> > +		WARN_ON(kprobe_disabled(&op->kp));
> > +
> > +		/*
> > +		 * Backup instructions which will be replaced
> > +		 * by jump address
> > +		 */
> > +		memcpy(op->optinsn.orig_insn, op->kp.addr, AARCH64_INSN_SIZE);
> > +
> > +		addrs[i] = (void *)op->kp.addr;
> > +		insns[i] = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr,
> > +						       (unsigned long)op->optinsn.trampoline,
> > +						       AARCH64_INSN_BRANCH_NOLINK);
> > +
> > +		list_del_init(&op->list);
> > +		if (++i == OPTPROBE_BATCH_SIZE)
> > +			break;
> > +	}
> > +
> > +	aarch64_insn_patch_text(addrs, insns, i);
> > +}
> > +
> > +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> > +{
> > +	arch_arm_kprobe(&op->kp);
> > +}
> > +
> > +/*
> > + * Recover original instructions and breakpoints from relative jumps.
> > + * Caller must call with locking kprobe_mutex.
> > + */
> > +void arch_unoptimize_kprobes(struct list_head *oplist,
> > +			    struct list_head *done_list)
> > +{
> > +	struct optimized_kprobe *op, *tmp;
> > +	kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE];
> > +	void *addrs[OPTPROBE_BATCH_SIZE];
> > +	int i = 0;
> > +
> > +	list_for_each_entry_safe(op, tmp, oplist, list) {
> > +		addrs[i] = (void *)op->kp.addr;
> > +		insns[i] = BRK64_OPCODE_KPROBES;
> > +		list_move(&op->list, done_list);
> > +
> > +		if (++i == OPTPROBE_BATCH_SIZE)
> > +			break;
> > +	}
> > +
> > +	aarch64_insn_patch_text(addrs, insns, i);
> > +}
> > +
> > +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
> > +{
> > +	if (op->optinsn.trampoline) {
> > +		free_optinsn_slot(op->optinsn.trampoline, 1);
> > +		op->optinsn.trampoline = NULL;
> > +	}
> > +}
> > diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S
> > new file mode 100644
> > index 000000000000..1376daeae844
> > --- /dev/null
> > +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
> > @@ -0,0 +1,97 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * trampoline entry and return code for optprobes.
> > + */
> > +
> > +#include <linux/linkage.h>
> > +#include <asm/asm-offsets.h>
> > +#include <asm/assembler.h>
> > +
> > +#define        OPT_SLOT_SIZE   65536
> > +
> > +	.global optinsn_slot
> > +optinsn_slot:
> > +	.space  OPT_SLOT_SIZE
> > +
> > +SYM_CODE_START(optprobe_common)
> > +	stp x2, x3, [sp, #S_X2]
> > +	stp x4, x5, [sp, #S_X4]
> > +	stp x6, x7, [sp, #S_X6]
> > +	stp x8, x9, [sp, #S_X8]
> > +	stp x10, x11, [sp, #S_X10]
> > +	stp x12, x13, [sp, #S_X12]
> > +	stp x14, x15, [sp, #S_X14]
> > +	stp x16, x17, [sp, #S_X16]
> > +	stp x18, x19, [sp, #S_X18]
> > +	stp x20, x21, [sp, #S_X20]
> > +	stp x22, x23, [sp, #S_X22]
> > +	stp x24, x25, [sp, #S_X24]
> > +	stp x26, x27, [sp, #S_X26]
> > +	stp x28, x29, [sp, #S_X28]
> > +	add x2, sp, #PT_REGS_SIZE
> > +	str x2, [sp, #S_SP]
> > +	/* Construct a useful saved PSTATE */
> > +	mrs x2, nzcv
> > +	mrs x3, daif
> > +	orr x2, x2, x3
> > +	mrs x3, CurrentEL
> > +	orr x2, x2, x3
> > +	mrs x3, SPSel
> > +	orr x2, x2, x3
> > +	stp xzr, x2, [sp, #S_PC]
> > +
> > +	/* set the pt_regs address to x1 */
> > +	mov	x1, sp
> > +	/* store lr of optprobe_common temporary */
> > +	sub sp, sp, #0x10
> > +	str lr, [sp, #0x8]
> > +
> > +	bl optprobe_optimized_callback
> > +
> > +	ldr lr, [sp, #0x8]
> > +	add sp, sp, #0x10
> > +	ldr x0, [sp, #S_PSTATE]
> > +	and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
> > +	msr nzcv, x0
> > +	ldp x0, x1, [sp, #S_X0]
> > +	ldp x2, x3, [sp, #S_X2]
> > +	ldp x4, x5, [sp, #S_X4]
> > +	ldp x6, x7, [sp, #S_X6]
> > +	ldp x8, x9, [sp, #S_X8]
> > +	ldp x10, x11, [sp, #S_X10]
> > +	ldp x12, x13, [sp, #S_X12]
> > +	ldp x14, x15, [sp, #S_X14]
> > +	ldp x16, x17, [sp, #S_X16]
> > +	ldp x18, x19, [sp, #S_X18]
> > +	ldp x20, x21, [sp, #S_X20]
> > +	ldp x22, x23, [sp, #S_X22]
> > +	ldp x24, x25, [sp, #S_X24]
> > +	ldp x26, x27, [sp, #S_X26]
> > +	ldp x28, x29, [sp, #S_X28]
> > +	ret
> > +SYM_CODE_END(optprobe_common)
> > +
> > +	.global optprobe_template_entry
> > +optprobe_template_entry:
> > +	sub sp, sp, #PT_REGS_SIZE
> > +	str lr, [sp, #S_LR]
> > +	stp x0, x1, [sp, #S_X0]
> > +	/* Get parameters to optimized_callback() */
> > +	ldr x0, 1f
> > +	.global optprobe_template_common
> > +optprobe_template_common:
> > +	nop
> > +	ldr lr, [sp, #S_LR]
> > +       add sp, sp, #PT_REGS_SIZE
> > +	.global optprobe_template_restore_orig_insn
> > +optprobe_template_restore_orig_insn:
> > +	nop
> > +	.global optprobe_template_restore_end
> > +optprobe_template_restore_end:
> > +	nop
> > +	.global optprobe_template_val
> > +optprobe_template_val:
> > +	1:	.long 0
> > +		.long 0
> > +	.global optprobe_template_end
> > +optprobe_template_end:
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 8c8f7a4d93af..7be680155df7 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -329,6 +329,7 @@ struct optimized_kprobe {
> >  	struct kprobe kp;
> >  	struct list_head list;	/* list for optimizing queue */
> >  	struct arch_optimized_insn optinsn;
> > +	void (*set_pc)(struct optimized_kprobe *op, struct pt_regs *regs);
> >  };
> >  
> >  /* Architecture dependent functions for direct jump optimization */
> > @@ -345,6 +346,7 @@ extern int arch_within_optimized_kprobe(struct optimized_kprobe *op,
> >  					kprobe_opcode_t *addr);
> >  
> >  extern void opt_pre_handler(struct kprobe *p, struct pt_regs *regs);
> > +extern void optprobe_optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs);
> >  
> >  DEFINE_INSN_CACHE_OPS(optinsn);
> >  
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 21eccc961bba..d799e562a39a 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -430,6 +430,28 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
> >  }
> >  NOKPROBE_SYMBOL(opt_pre_handler);
> >  
> > +void optprobe_optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
> > +{
> > +	if (kprobe_disabled(&op->kp))
> > +		return;
> > +
> > +	preempt_disable();
> > +
> > +	if (kprobe_running()) {
> > +		kprobes_inc_nmissed_count(&op->kp);
> > +	} else {
> > +		op->set_pc(op, regs);
> > +		__this_cpu_write(current_kprobe, &op->kp);
> > +		get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> > +		opt_pre_handler(&op->kp, regs);
> > +		__this_cpu_write(current_kprobe, NULL);
> > +	}
> > +
> > +	preempt_enable();
> > +}
> > +NOKPROBE_SYMBOL(optprobe_optimized_callback)
> > +
> > +
> >  /* Free optimized instructions and optimized_kprobe */
> >  static void free_aggr_kprobe(struct kprobe *p)
> >  {
> > -- 
> > 2.33.0
> > 


-- 
Masami Hiramatsu <mhiramat@...nel.org>

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