uprobes/x86: Add support to emulate NOP instructions

JIRA: https://issues.redhat.com/browse/RHEL-78203

commit 610f6e1
Author: Jiri Olsa <jolsa@kernel.org>
Date:   Mon Apr 14 10:36:46 2025 +0200

    uprobes/x86: Add support to emulate NOP instructions

    Add support to emulate all NOP instructions as the original uprobe
    instruction.

    This change speeds up uprobe on top of all NOP instructions and is a
    preparation for usdt probe optimization, that will be done on top of
    NOP5 instructions.

    With this change the usdt probe on top of NOP5s won't take the performance
    hit compared to usdt probe on top of standard NOP instructions.

    Suggested-by: Oleg Nesterov <oleg@redhat.com>
    Suggested-by: Andrii Nakryiko <andrii@kernel.org>
    Signed-off-by: Jiri Olsa <jolsa@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Reviewed-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Andrii Nakryiko <andrii@kernel.org>
    Cc: Alan Maguire <alan.maguire@oracle.com>
    Cc: Hao Luo <haoluo@google.com>
    Cc: John Fastabend <john.fastabend@gmail.com>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Song Liu <songliubraving@fb.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Yonghong Song <yhs@fb.com>
    Link: https://lore.kernel.org/r/20250414083647.1234007-1-jolsa@kernel.org

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Author: viktormalik

arch/x86/kernel/uprobes.c

@@ -836,6 +836,11 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 	insn_byte_t p;
 	int i;
 
+	/* x86_nops[insn->length]; same as jmp with .offs = 0 */
+	if (insn->length <= ASM_NOP_MAX &&
+	    !memcmp(insn->kaddr, x86_nops[insn->length], insn->length))
+		goto setup;
+
 	switch (opc1) {
 	case 0xeb:	/* jmp 8 */
 	case 0xe9:	/* jmp 32 */