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Message-ID: <56241cbe-228b-9e7d-82c8-5578fa9ee3eb@loongson.cn>
Date: Fri, 9 Dec 2022 14:10:10 +0800
From: Youling Tang <tangyouling@...ngson.cn>
To: Jinyang He <hejinyang@...ngson.cn>,
Huacai Chen <chenhuacai@...nel.org>,
Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>,
Masami Hiramatsu <mhiramat@...nel.org>,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/4] LoongArch: Add kprobe support
On 12/09/2022 01:53 PM, Jinyang He wrote:
> On 2022-12-09 11:44, Youling Tang wrote:
>
>> Hi, Jinyang
>>
>> On 12/09/2022 11:31 AM, Jinyang He wrote:
>>> On 2022-12-09 10:22, Huacai Chen wrote:
>>>
>>>> cas
>>>>
>>>> On Thu, Dec 8, 2022 at 9:41 PM Tiezhu Yang <yangtiezhu@...ngson.cn>
>>>> wrote:
>>>>> Kprobes allows you to trap at almost any kernel address and
>>>>> execute a callback function, this commit adds kprobe support
>>>>> for LoongArch.
>>>>>
>>>>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>>>>> ---
>>>>> arch/loongarch/Kconfig | 1 +
>>>>> arch/loongarch/include/asm/inst.h | 15 ++
>>>>> arch/loongarch/include/asm/kprobes.h | 59 +++++++
>>>>> arch/loongarch/kernel/Makefile | 2 +
>>>>> arch/loongarch/kernel/kprobes.c | 332
>>>>> +++++++++++++++++++++++++++++++++++
>>>>> arch/loongarch/kernel/traps.c | 13 +-
>>>>> arch/loongarch/mm/fault.c | 3 +
>>>>> 7 files changed, 421 insertions(+), 4 deletions(-)
>>>>> create mode 100644 arch/loongarch/include/asm/kprobes.h
>>>>> create mode 100644 arch/loongarch/kernel/kprobes.c
>>>>>
>>>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>>>> index 16bf1b6..f6fc156 100644
>>>>> --- a/arch/loongarch/Kconfig
>>>>> +++ b/arch/loongarch/Kconfig
>>>>> @@ -102,6 +102,7 @@ config LOONGARCH
>>>>> select HAVE_IOREMAP_PROT
>>>>> select HAVE_IRQ_EXIT_ON_IRQ_STACK
>>>>> select HAVE_IRQ_TIME_ACCOUNTING
>>>>> + select HAVE_KPROBES
>>>>> select HAVE_MOD_ARCH_SPECIFIC
>>>>> select HAVE_NMI
>>>>> select HAVE_PCI
>>>>> diff --git a/arch/loongarch/include/asm/inst.h
>>>>> b/arch/loongarch/include/asm/inst.h
>>>>> index 19cf692..e3f2378 100644
>>>>> --- a/arch/loongarch/include/asm/inst.h
>>>>> +++ b/arch/loongarch/include/asm/inst.h
>>>>> @@ -24,6 +24,10 @@
>>>>>
>>>>> #define ADDR_IMM(addr, INSN) ((addr & ADDR_IMMMASK_##INSN) >>
>>>>> ADDR_IMMSHIFT_##INSN)
>>>>>
>>>>> +enum reg0i15_op {
>>>>> + break_op = 0x54,
>>>>> +};
>>>>> +
>>>>> enum reg0i26_op {
>>>>> b_op = 0x14,
>>>>> bl_op = 0x15,
>>>>> @@ -180,6 +184,11 @@ enum reg3sa2_op {
>>>>> alsld_op = 0x16,
>>>>> };
>>>>>
>>>>> +struct reg0i15_format {
>>>>> + unsigned int immediate : 15;
>>>>> + unsigned int opcode : 17;
>>>>> +};
>>>>> +
>>>>> struct reg0i26_format {
>>>>> unsigned int immediate_h : 10;
>>>>> unsigned int immediate_l : 16;
>>>>> @@ -265,6 +274,7 @@ struct reg3sa2_format {
>>>>>
>>>>> union loongarch_instruction {
>>>>> unsigned int word;
>>>>> + struct reg0i15_format reg0i15_format;
>>>>> struct reg0i26_format reg0i26_format;
>>>>> struct reg1i20_format reg1i20_format;
>>>>> struct reg1i21_format reg1i21_format;
>>>>> @@ -335,6 +345,11 @@ static inline bool is_branch_ins(union
>>>>> loongarch_instruction *ip)
>>>>> ip->reg1i21_format.opcode <= bgeu_op;
>>>>> }
>>>>>
>>>>> +static inline bool is_break_ins(union loongarch_instruction *ip)
>>>>> +{
>>>>> + return ip->reg0i15_format.opcode == break_op;
>>>>> +}
>>>>> +
>>>>> static inline bool is_ra_save_ins(union loongarch_instruction *ip)
>>>>> {
>>>>> /* st.d $ra, $sp, offset */
>>>>> diff --git a/arch/loongarch/include/asm/kprobes.h
>>>>> b/arch/loongarch/include/asm/kprobes.h
>>>>> new file mode 100644
>>>>> index 0000000..d3903f3
>>>>> --- /dev/null
>>>>> +++ b/arch/loongarch/include/asm/kprobes.h
>>>>> @@ -0,0 +1,59 @@
>>>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>>>> +#ifndef __ASM_LOONGARCH_KPROBES_H
>>>>> +#define __ASM_LOONGARCH_KPROBES_H
>>>>> +
>>>>> +#include <asm-generic/kprobes.h>
>>>>> +#include <asm/cacheflush.h>
>>>>> +
>>>>> +#ifdef CONFIG_KPROBES
>>>>> +
>>>>> +#include <asm/inst.h>
>>>>> +
>>>>> +#define __ARCH_WANT_KPROBES_INSN_SLOT
>>>>> +#define MAX_INSN_SIZE 2
>>>>> +
>>>>> +#define
>>>>> flush_insn_slot(p) \
>>>>> +do
>>>>> { \
>>>>> + if
>>>>> (p->addr) \
>>>>> + flush_icache_range((unsigned
>>>>> long)p->addr, \
>>>>> + (unsigned long)p->addr
>>>>> + \
>>>>> + (MAX_INSN_SIZE *
>>>>> sizeof(kprobe_opcode_t))); \
>>>>> +} while (0)
>>>>> +
>>>>> +#define kretprobe_blacklist_size 0
>>>>> +
>>>>> +typedef union loongarch_instruction kprobe_opcode_t;
>>>>> +
>>>>> +/* Architecture specific copy of original instruction */
>>>>> +struct arch_specific_insn {
>>>>> + /* copy of the original instruction */
>>>>> + kprobe_opcode_t *insn;
>>>>> +};
>>>>> +
>>>>> +struct prev_kprobe {
>>>>> + struct kprobe *kp;
>>>>> + unsigned long status;
>>>>> + unsigned long saved_irq;
>>>>> + unsigned long saved_era;
>>>>> +};
>>>>> +
>>>>> +/* per-cpu kprobe control block */
>>>>> +struct kprobe_ctlblk {
>>>>> + unsigned long kprobe_status;
>>>>> + unsigned long kprobe_saved_irq;
>>>>> + unsigned long kprobe_saved_era;
>>>>> + struct prev_kprobe prev_kprobe;
>>>>> +};
>>>>> +
>>>>> +void arch_remove_kprobe(struct kprobe *p);
>>>>> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr);
>>>>> +bool kprobe_breakpoint_handler(struct pt_regs *regs);
>>>>> +bool kprobe_singlestep_handler(struct pt_regs *regs);
>>>>> +
>>>>> +#else /* !CONFIG_KPROBES */
>>>>> +
>>>>> +static inline bool kprobe_breakpoint_handler(struct pt_regs *regs) {
>>>>> return 0; }
>>>>> +static inline bool kprobe_singlestep_handler(struct pt_regs *regs) {
>>>>> return 0; }
>>>>> +
>>>>> +#endif /* CONFIG_KPROBES */
>>>>> +#endif /* __ASM_LOONGARCH_KPROBES_H */
>>>>> diff --git a/arch/loongarch/kernel/Makefile
>>>>> b/arch/loongarch/kernel/Makefile
>>>>> index fcaa024..6fe4a4e 100644
>>>>> --- a/arch/loongarch/kernel/Makefile
>>>>> +++ b/arch/loongarch/kernel/Makefile
>>>>> @@ -47,4 +47,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>>>>>
>>>>> obj-$(CONFIG_PERF_EVENTS) += perf_event.o perf_regs.o
>>>>>
>>>>> +obj-$(CONFIG_KPROBES) += kprobes.o
>>>>> +
>>>>> CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
>>>>> diff --git a/arch/loongarch/kernel/kprobes.c
>>>>> b/arch/loongarch/kernel/kprobes.c
>>>>> new file mode 100644
>>>>> index 0000000..aadfc9ae
>>>>> --- /dev/null
>>>>> +++ b/arch/loongarch/kernel/kprobes.c
>>>>> @@ -0,0 +1,332 @@
>>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>>> +#include <linux/kprobes.h>
>>>>> +#include <linux/kdebug.h>
>>>>> +#include <linux/preempt.h>
>>>>> +#include <asm/break.h>
>>>>> +
>>>>> +static const union loongarch_instruction breakpoint_insn = {
>>>>> + .reg0i15_format = {
>>>>> + .opcode = break_op,
>>>>> + .immediate = BRK_KPROBE_BP,
>>>>> + }
>>>>> +};
>>>>> +
>>>>> +static const union loongarch_instruction singlestep_insn = {
>>>>> + .reg0i15_format = {
>>>>> + .opcode = break_op,
>>>>> + .immediate = BRK_KPROBE_SSTEPBP,
>>>>> + }
>>>>> +};
>>>>> +
>>>>> +DEFINE_PER_CPU(struct kprobe *, current_kprobe);
>>>>> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>>>> +
>>>>> +static bool insns_are_not_supported(union loongarch_instruction insn)
>>>> Use insns_not_supported for short.
>>>>
>>>>> +{
>>>>> + switch (insn.reg2i14_format.opcode) {
>>>>> + case llw_op:
>>>>> + case lld_op:
>>>>> + case scw_op:
>>>>> + case scd_op:
>>>>> + pr_notice("kprobe: ll and sc instructions are not
>>>>> supported\n");
>>>>> + return true;
>>>>> + }
>>>>> +
>>>>> + switch (insn.reg1i21_format.opcode) {
>>>>> + case bceqz_op:
>>>>> + pr_notice("kprobe: bceqz and bcnez instructions are
>>>>> not supported\n");
>>>>> + return true;
>>>>> + }
>>>>> +
>>>>> + return false;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(insns_are_not_supported);
>>>>> +
>>>>> +int arch_prepare_kprobe(struct kprobe *p)
>>>>> +{
>>>>> + union loongarch_instruction insn;
>>>>> +
>>>>> + insn = p->addr[0];
>>>>> + if (insns_are_not_supported(insn))
>>>>> + return -EINVAL;
>>>>> +
>>>>> + p->ainsn.insn = get_insn_slot();
>>>>> + if (!p->ainsn.insn)
>>>>> + return -ENOMEM;
>>>>> +
>>>>> + p->ainsn.insn[0] = *p->addr;
>>>>> + p->ainsn.insn[1] = singlestep_insn;
>>>>> +
>>>>> + p->opcode = *p->addr;
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(arch_prepare_kprobe);
>>>>> +
>>>>> +/* Install breakpoint in text */
>>>>> +void arch_arm_kprobe(struct kprobe *p)
>>>>> +{
>>>>> + *p->addr = breakpoint_insn;
>>>>> + flush_insn_slot(p);
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(arch_arm_kprobe);
>>>>> +
>>>>> +/* Remove breakpoint from text */
>>>>> +void arch_disarm_kprobe(struct kprobe *p)
>>>>> +{
>>>>> + *p->addr = p->opcode;
>>>>> + flush_insn_slot(p);
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(arch_disarm_kprobe);
>>>>> +
>>>>> +void arch_remove_kprobe(struct kprobe *p)
>>>>> +{
>>>>> + if (p->ainsn.insn) {
>>>>> + free_insn_slot(p->ainsn.insn, 0);
>>>>> + p->ainsn.insn = NULL;
>>>>> + }
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(arch_remove_kprobe);
>>>>> +
>>>>> +static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
>>>>> +{
>>>>> + kcb->prev_kprobe.kp = kprobe_running();
>>>>> + kcb->prev_kprobe.status = kcb->kprobe_status;
>>>>> + kcb->prev_kprobe.saved_irq = kcb->kprobe_saved_irq;
>>>>> + kcb->prev_kprobe.saved_era = kcb->kprobe_saved_era;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(save_previous_kprobe);
>>>>> +
>>>>> +static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
>>>>> +{
>>>>> + __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
>>>>> + kcb->kprobe_status = kcb->prev_kprobe.status;
>>>>> + kcb->kprobe_saved_irq = kcb->prev_kprobe.saved_irq;
>>>>> + kcb->kprobe_saved_era = kcb->prev_kprobe.saved_era;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(restore_previous_kprobe);
>>>>> +
>>>>> +static void set_current_kprobe(struct kprobe *p, struct pt_regs
>>>>> *regs,
>>>>> + struct kprobe_ctlblk *kcb)
>>>>> +{
>>>>> + __this_cpu_write(current_kprobe, p);
>>>>> + kcb->kprobe_saved_irq = regs->csr_prmd & CSR_PRMD_PIE;
>>>>> + kcb->kprobe_saved_era = regs->csr_era;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(set_current_kprobe);
>>>>> +
>>>>> +static bool insns_are_not_simulated(struct kprobe *p, struct pt_regs
>>>>> *regs)
>>>> Use insns_not_simulated for short.
>>>>> +{
>>>>> + if (is_branch_ins(&p->opcode)) {
>>>>> + simu_branch(regs, p->opcode);
>>>>> + return false;
>>>>> + } else if (is_pc_ins(&p->opcode)) {
>>>>> + simu_pc(regs, p->opcode);
>>>>> + return false;
>>>>> + } else {
>>>>> + return true;
>>>>> + }
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(insns_are_not_simulated);
>>>>> +
>>>>> +static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
>>>>> + struct kprobe_ctlblk *kcb, int reenter)
>>>>> +{
>>>>> + if (reenter) {
>>>>> + save_previous_kprobe(kcb);
>>>>> + set_current_kprobe(p, regs, kcb);
>>>>> + kcb->kprobe_status = KPROBE_REENTER;
>>>>> + } else {
>>>>> + kcb->kprobe_status = KPROBE_HIT_SS;
>>>>> + }
>>>>> +
>>>>> + regs->csr_prmd &= ~CSR_PRMD_PIE;
>>>>> +
>>>>> + if (p->ainsn.insn->word == breakpoint_insn.word) {
>>>>> + regs->csr_prmd |= kcb->kprobe_saved_irq;
>>>>> + preempt_enable_no_resched();
>>>>> + return;
>>>>> + }
>>>>> +
>>>>> + if (insns_are_not_simulated(p, regs)) {
>>>>> + kcb->kprobe_status = KPROBE_HIT_SS;
>>>>> + regs->csr_era = (unsigned long)&p->ainsn.insn[0];
>>>>> + } else {
>>>>> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
>>>>> + if (p->post_handler)
>>>>> + p->post_handler(p, regs, 0);
>>>>> + reset_current_kprobe();
>>>>> + preempt_enable_no_resched();
>>>>> + }
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(setup_singlestep);
>>>>> +
>>>>> +static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
>>>>> + struct kprobe_ctlblk *kcb)
>>>>> +{
>>>>> + switch (kcb->kprobe_status) {
>>>>> + case KPROBE_HIT_SSDONE:
>>>>> + case KPROBE_HIT_ACTIVE:
>>>>> + kprobes_inc_nmissed_count(p);
>>>>> + setup_singlestep(p, regs, kcb, 1);
>>>>> + break;
>>>>> + case KPROBE_HIT_SS:
>>>>> + case KPROBE_REENTER:
>>>>> + pr_warn("Failed to recover from reentered
>>>>> kprobes.\n");
>>>>> + dump_kprobe(p);
>>>>> + BUG();
>>>>> + break;
>>>>> + default:
>>>>> + WARN_ON(1);
>>>>> + return false;
>>>>> + }
>>>>> +
>>>>> + return true;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(reenter_kprobe);
>>>>> +
>>>>> +bool kprobe_breakpoint_handler(struct pt_regs *regs)
>>>>> +{
>>>>> + struct kprobe_ctlblk *kcb;
>>>>> + struct kprobe *p, *cur_kprobe;
>>>>> + kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->csr_era;
>>>>> +
>>>>> + /*
>>>>> + * We don't want to be preempted for the entire
>>>>> + * duration of kprobe processing.
>>>>> + */
>>>>> + preempt_disable();
>>>>> + kcb = get_kprobe_ctlblk();
>>>>> + cur_kprobe = kprobe_running();
>>>>> +
>>>>> + p = get_kprobe(addr);
>>>>> + if (p) {
>>>>> + if (cur_kprobe) {
>>>>> + if (reenter_kprobe(p, regs, kcb))
>>>>> + return true;
>>>>> + } else {
>>>>> + /* Probe hit */
>>>>> + set_current_kprobe(p, regs, kcb);
>>>>> + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
>>>>> +
>>>>> + /*
>>>>> + * If we have no pre-handler or it returned
>>>>> 0, we
>>>>> + * continue with normal processing. If we
>>>>> have a
>>>>> + * pre-handler and it returned non-zero, it
>>>>> will
>>>>> + * modify the execution path and no need to
>>>>> single
>>>>> + * stepping. Let's just reset current kprobe
>>>>> and exit.
>>>>> + *
>>>>> + * pre_handler can hit a breakpoint and can
>>>>> step thru
>>>>> + * before return.
>>>>> + */
>>>>> + if (!p->pre_handler || !p->pre_handler(p,
>>>>> regs)) {
>>>>> + setup_singlestep(p, regs, kcb, 0);
>>>>> + } else {
>>>>> + reset_current_kprobe();
>>>>> + preempt_enable_no_resched();
>>>>> + }
>>>>> + }
>>>>> + return true;
>>>>> + }
>>>>> +
>>>>> + if (!is_break_ins(addr)) {
>>>>> + /*
>>>>> + * The breakpoint instruction was removed right
>>>>> + * after we hit it. Another cpu has removed
>>>>> + * either a probepoint or a debugger breakpoint
>>>>> + * at this address. In either case, no further
>>>>> + * handling of this interrupt is appropriate.
>>>>> + * Return back to original instruction, and continue.
>>>>> + */
>>>>> + preempt_enable_no_resched();
>>>>> + return true;
>>>>> + }
>>>>> +
>>>>> + preempt_enable_no_resched();
>>>>> + return false;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(kprobe_breakpoint_handler);
>>>>> +
>>>>> +bool kprobe_singlestep_handler(struct pt_regs *regs)
>>>>> +{
>>>>> + struct kprobe *cur = kprobe_running();
>>>>> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>>>>> +
>>>>> + if (!cur)
>>>>> + return false;
>>>>> +
>>>>> + /* Restore back the original saved kprobes variables and
>>>>> continue */
>>>>> + if (kcb->kprobe_status == KPROBE_REENTER) {
>>>>> + restore_previous_kprobe(kcb);
>>>>> + goto out;
>>>>> + }
>>>>> +
>>>>> + /* Call post handler */
>>>>> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
>>>>> + if (cur->post_handler)
>>>>> + cur->post_handler(cur, regs, 0);
>>>> I'm not very familiar, but I think you should set KPROBE_HIT_SSDONE
>>>> only when post_handler is not NULL.
>>>>
>>>>> +
>>>>> + regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
>>>>> + regs->csr_prmd |= kcb->kprobe_saved_irq;
>>>>> +
>>>>> + reset_current_kprobe();
>>>>> +out:
>>>>> + preempt_enable_no_resched();
>>>>> + return true;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(kprobe_singlestep_handler);
>>>>> +
>>>>> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
>>>>> +{
>>>>> + struct kprobe *cur = kprobe_running();
>>>>> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>>>>> +
>>>>> + switch (kcb->kprobe_status) {
>>>>> + case KPROBE_HIT_SS:
>>>>> + case KPROBE_REENTER:
>>>>> + /*
>>>>> + * We are here because the instruction being single
>>>>> + * stepped caused a page fault. We reset the current
>>>>> + * kprobe and the ip points back to the probe address
>>>>> + * and allow the page fault handler to continue as a
>>>>> + * normal page fault.
>>>>> + */
>>>>> + regs->csr_era = (unsigned long) cur->addr;
>>>>> + BUG_ON(!instruction_pointer(regs));
>>>>> +
>>>>> + if (kcb->kprobe_status == KPROBE_REENTER) {
>>>>> + restore_previous_kprobe(kcb);
>>>>> + } else {
>>>>> + regs->csr_prmd |= kcb->kprobe_saved_irq;
>>>>> + reset_current_kprobe();
>>>>> + preempt_enable_no_resched();
>>>>> + }
>>>> I think the KPROBE_REENTER case also needs to enable preemption.
>>>>
>>>>> +
>>>>> + break;
>>>>> + case KPROBE_HIT_ACTIVE:
>>>>> + case KPROBE_HIT_SSDONE:
>>>>> + /*
>>>>> + * In case the user-specified fault handler returned
>>>>> + * zero, try to fix up.
>>>>> + */
>>>>> + if (fixup_exception(regs))
>>>>> + return true;
>>>> Does here need to enable preemption too?
>>>>
>>>>> + }
>>>>> + return false;
>>>>> +}
>>>>> +NOKPROBE_SYMBOL(kprobe_fault_handler);
>>>>> +
>>>>> +/*
>>>>> + * Provide a blacklist of symbols identifying ranges which cannot be
>>>>> kprobed.
>>>>> + * This blacklist is exposed to userspace via debugfs
>>>>> (kprobes/blacklist).
>>>>> + */
>>>>> +int __init arch_populate_kprobe_blacklist(void)
>>>>> +{
>>>>> + return kprobe_add_area_blacklist((unsigned
>>>>> long)__irqentry_text_start,
>>>>> + (unsigned
>>>>> long)__irqentry_text_end);
>>>>> +}
>>>>> +
>>>>> +int __init arch_init_kprobes(void)
>>>>> +{
>>>>> + return 0;
>>>>> +}
>>>>> diff --git a/arch/loongarch/kernel/traps.c
>>>>> b/arch/loongarch/kernel/traps.c
>>>>> index a19bb32..4d9f775 100644
>>>>> --- a/arch/loongarch/kernel/traps.c
>>>>> +++ b/arch/loongarch/kernel/traps.c
>>>>> @@ -448,14 +448,12 @@ asmlinkage void noinstr do_bp(struct pt_regs
>>>>> *regs)
>>>>> */
>>>>> switch (bcode) {
>>>>> case BRK_KPROBE_BP:
>>>>> - if (notify_die(DIE_BREAK, "Kprobe", regs, bcode,
>>>>> - current->thread.trap_nr, SIGTRAP) ==
>>>>> NOTIFY_STOP)
>>>>> + if (kprobe_breakpoint_handler(regs))
>>>>> goto out;
>>>>> else
>>>>> break;
>>>>> case BRK_KPROBE_SSTEPBP:
>>>>> - if (notify_die(DIE_SSTEPBP, "Kprobe_SingleStep",
>>>>> regs, bcode,
>>>>> - current->thread.trap_nr, SIGTRAP) ==
>>>>> NOTIFY_STOP)
>>>>> + if (kprobe_singlestep_handler(regs))
>>>>> goto out;
>>>>> else
>>>>> break;
>>>>> @@ -479,6 +477,13 @@ asmlinkage void noinstr do_bp(struct pt_regs
>>>>> *regs)
>>>>> break;
>>>>> }
>>>>>
>>>>> + if (bcode == BRK_KPROBE_BP) {
>>>>> + if (__get_inst(&opcode, (u32 *)era, user))
>>>>> + goto out_sigsegv;
>>>>> +
>>>>> + bcode = (opcode & 0x7fff);
>>>>> + }
>>>>> +
>>>> Why? we already got bcode at the beginning.
>>>
>>> Hi, Huacai,
>>>
>>>
>>> I think it is because kprobe_breakpoint_handler() may deal with that
>>> case other cpu may remove its breakpoint. In that case, normally we can
>>> exit this break exception and go on. But if
>>> the orignal instruction is_break_ins(), we will trigger trap aggain. So
>>> it is better to avoid double traps and let it go ahead when
>>> kprobe_breakpoint_handler() returns.
>> Perhaps it is not described here as avoiding the trap twice,
>
> That due to the implementation in the last branch, is_break_ins(), in
> kprobe_breakpoint_handler(). We can indirectly return true for all
> instructions to indicate we can stop kprobe now.
> And then it returns the normal code flow. If the instruction at ERA is a
> "break xxx", it would traps again. I call it as "trap twice" because at
> here we are in the fisrt time trap.
Mmm, it can be understood that way.
Thanks.
> To avoid the second trap, we add the judgment named is_break_ins() and
> return false to indicate we should go another break handler. Of course,
> with the instruction being restored, we should re-get the bcode.
>
>
>> but rather
>> that if we don't re-fetch the bcode when the original instruction
>> `break` will go to the default branch regardless of what the bcode of
>> the original instruction is (since the bcode is BRK_KPROBE_BP at this
>> point). IMHO, so we re-get the bcode to get the original instruction
>> `break` is the correct bcode to ensure that it goes to the appropriate
>> case branch.
>>
>> Thanks,
>> Youling.
>>
>>> Differnt from many other archs, e.g. riscv, we switch bcode to decide
>>> which handlers should go on. Thus, we need get bcode again.
>>>
>>> Thanks,
>>>
>>> Jinyang
>>>
>>>
>>>>> switch (bcode) {
>>>>> case BRK_BUG:
>>>>> bug_handler(regs);
>>>>> diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
>>>>> index 1ccd536..449087b 100644
>>>>> --- a/arch/loongarch/mm/fault.c
>>>>> +++ b/arch/loongarch/mm/fault.c
>>>>> @@ -135,6 +135,9 @@ static void __kprobes __do_page_fault(struct
>>>>> pt_regs *regs,
>>>>> struct vm_area_struct *vma = NULL;
>>>>> vm_fault_t fault;
>>>>>
>>>>> + if (kprobe_page_fault(regs, current->thread.trap_nr))
>>>>> + return;
>>>>> +
>>>>> /*
>>>>> * We fault-in kernel-space virtual memory on-demand. The
>>>>> * 'reference' page table is init_mm.pgd.
>>>>> --
>>>>> 2.1.0
>>>>>
>>>>>
>>>
>
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