[PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64
Will Deacon
will at kernel.org
Mon Dec 13 10:38:52 PST 2021
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 at kernel.org>
> Signed-off-by: Qi Liu <liuqi115 at huawei.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
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.
Cheers,
Will
[Kept diff inline for Janet]
> 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
>
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