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a8497506cd
get_kernel_nofault() (or, rather, underlying copy_from_kernel_nofault()) is not free and it does pop up in performance profiles when kprobes are heavily utilized with CONFIG_X86_KERNEL_IBT=y config. Let's avoid using it if we know that fentry_ip - 4 can't cross page boundary. We do that by masking lowest 12 bits and checking if they are Another benefit (and actually what caused a closer look at this part of code) is that now LBR record is (typically) not wasted on copy_from_kernel_nofault() call and code, which helps tools like retsnoop that grab LBR records from inside BPF code in kretprobes. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Jiri Olsa <jolsa@kernel.org> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Link: https://lore.kernel.org/bpf/20240319212013.1046779-1-andrii@kernel.org