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Message-Id: <20230126161559.1467374-1-guoren@kernel.org>
Date: Thu, 26 Jan 2023 11:15:59 -0500
From: guoren@...nel.org
To: guoren@...nel.org, palmer@...belt.com, paul.walmsley@...ive.com,
mhiramat@...nel.org, conor.dooley@...rochip.com,
penberg@...nel.org, mark.rutland@....com
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH] riscv: kprobe: Optimize kprobe with accurate atomicity
From: Guo Ren <guoren@...ux.alibaba.com>
The previous implementation was based on the stop_matchine mechanism,
which reduced the speed of arm/disarm_kprobe. Using minimum ebreak
instruction would get accurate atomicity.
This patch removes the patch_text of riscv, which is based on
stop_machine. Then riscv only reserved patch_text_nosync, and developers
need to be more careful in dealing with patch_text atomicity.
When CONFIG_RISCV_ISA_C=n, the ebreak could replace the whole
instruction. When CONFIG_RISCV_ISA_C=y, the patch uses 16-bit length
c.ebreak instruction, which may occupy the first part of the 32-bit
instruction and leave half the rest of the broken instruction. Because
ebreak could detour the flow to skip it, leaving it in the kernel text
memory is okay.
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
---
arch/riscv/include/asm/patch.h | 1 -
arch/riscv/kernel/patch.c | 33 ------------------------------
arch/riscv/kernel/probes/kprobes.c | 29 ++++++++++++++++++--------
3 files changed, 21 insertions(+), 42 deletions(-)
diff --git a/arch/riscv/include/asm/patch.h b/arch/riscv/include/asm/patch.h
index 9a7d7346001e..2500782e6f5b 100644
--- a/arch/riscv/include/asm/patch.h
+++ b/arch/riscv/include/asm/patch.h
@@ -7,6 +7,5 @@
#define _ASM_RISCV_PATCH_H
int patch_text_nosync(void *addr, const void *insns, size_t len);
-int patch_text(void *addr, u32 insn);
#endif /* _ASM_RISCV_PATCH_H */
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 765004b60513..8bd51ed8b806 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -98,36 +98,3 @@ int patch_text_nosync(void *addr, const void *insns, size_t len)
return ret;
}
NOKPROBE_SYMBOL(patch_text_nosync);
-
-static int patch_text_cb(void *data)
-{
- struct patch_insn *patch = data;
- int ret = 0;
-
- if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
- ret =
- patch_text_nosync(patch->addr, &patch->insn,
- GET_INSN_LENGTH(patch->insn));
- atomic_inc(&patch->cpu_count);
- } else {
- while (atomic_read(&patch->cpu_count) <= num_online_cpus())
- cpu_relax();
- smp_mb();
- }
-
- return ret;
-}
-NOKPROBE_SYMBOL(patch_text_cb);
-
-int patch_text(void *addr, u32 insn)
-{
- struct patch_insn patch = {
- .addr = addr,
- .insn = insn,
- .cpu_count = ATOMIC_INIT(0),
- };
-
- return stop_machine_cpuslocked(patch_text_cb,
- &patch, cpu_online_mask);
-}
-NOKPROBE_SYMBOL(patch_text);
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 475989f06d6d..27f8960c321c 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -24,12 +24,18 @@ 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);
+#ifdef CONFIG_RISCV_ISA_C
+ u32 opcode = __BUG_INSN_16;
+#else
+ u32 opcode = __BUG_INSN_32;
+#endif
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);
+ patch_text_nosync(p->ainsn.api.insn, &p->opcode, offset);
+ patch_text_nosync((void *)((unsigned long)(p->ainsn.api.insn) + offset),
+ &opcode, GET_INSN_LENGTH(opcode));
+
}
static void __kprobes arch_prepare_simulate(struct kprobe *p)
@@ -114,16 +120,23 @@ void *alloc_insn_page(void)
/* install breakpoint in text */
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
- if ((p->opcode & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
- patch_text(p->addr, __BUG_INSN_32);
- else
- patch_text(p->addr, __BUG_INSN_16);
+#ifdef CONFIG_RISCV_ISA_C
+ u32 opcode = __BUG_INSN_16;
+#else
+ u32 opcode = __BUG_INSN_32;
+#endif
+ patch_text_nosync(p->addr, &opcode, GET_INSN_LENGTH(opcode));
}
/* remove breakpoint from text */
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
- patch_text(p->addr, p->opcode);
+#ifdef CONFIG_RISCV_ISA_C
+ u32 opcode = __BUG_INSN_16;
+#else
+ u32 opcode = __BUG_INSN_32;
+#endif
+ patch_text_nosync(p->addr, &p->opcode, GET_INSN_LENGTH(opcode));
}
void __kprobes arch_remove_kprobe(struct kprobe *p)
--
2.36.1
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