linux-kernel - [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot

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Message-ID: <20220907023327.85630-1-liaochang1@huawei.com>
Date:   Wed, 7 Sep 2022 10:33:27 +0800
From:   Liao Chang <liaochang1@...wei.com>
To:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <mhiramat@...nel.org>,
        <rostedt@...dmis.org>, <liaochang1@...wei.com>
CC:     <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot

Since no race condition occurs on each instruction slot, hence it is
safe to patch instruction slot without stopping machine.

Signed-off-by: Liao Chang <liaochang1@...wei.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..eff7d7fab535 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);
+	const kprobe_opcode_t brk_insn = __BUG_INSN_32;
+	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);
+	memcpy((void *)((unsigned long)slot + offset), &brk_insn, 4);
+	patch_text_nosync(p->ainsn.api.insn, slot, offset + 4);
 }
 
 static void __kprobes arch_prepare_simulate(struct kprobe *p)
-- 
2.17.1