linux-kernel - Re: [PATCH bpf-next v3 1/2] arm64: stacktrace: Implement arch_bpf_stack

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Message-ID: <ZdegTX9x2ye-7xIt@arm.com>
Date: Thu, 22 Feb 2024 19:28:13 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Puranjay Mohan <puranjay12@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Zi Shen Lim <zlim.lnx@...il.com>, Will Deacon <will@...nel.org>,
	bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH bpf-next v3 1/2] arm64: stacktrace: Implement
 arch_bpf_stack_walk() for the BPF JIT

On Thu, Feb 01, 2024 at 12:52:24PM +0000, Puranjay Mohan wrote:
> This will be used by bpf_throw() to unwind till the program marked as
> exception boundary and run the callback with the stack of the main
> program.
> 
> This is required for supporting BPF exceptions on ARM64.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
> ---
>  arch/arm64/kernel/stacktrace.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 7f88028a00c0..66cffc5fc0be 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -7,6 +7,7 @@
>  #include <linux/kernel.h>
>  #include <linux/efi.h>
>  #include <linux/export.h>
> +#include <linux/filter.h>
>  #include <linux/ftrace.h>
>  #include <linux/kprobes.h>
>  #include <linux/sched.h>
> @@ -266,6 +267,31 @@ noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
>  	kunwind_stack_walk(arch_kunwind_consume_entry, &data, task, regs);
>  }
>  
> +struct bpf_unwind_consume_entry_data {
> +	bool (*consume_entry)(void *cookie, u64 ip, u64 sp, u64 fp);
> +	void *cookie;
> +};
> +
> +static bool
> +arch_bpf_unwind_consume_entry(const struct kunwind_state *state, void *cookie)
> +{
> +	struct bpf_unwind_consume_entry_data *data = cookie;
> +
> +	return data->consume_entry(data->cookie, state->common.pc, 0,
> +				   state->common.fp);
> +}
> +
> +noinline noinstr void arch_bpf_stack_walk(bool (*consume_entry)(void *cookie, u64 ip, u64 sp,
> +								u64 fp), void *cookie)
> +{
> +	struct bpf_unwind_consume_entry_data data = {
> +		.consume_entry = consume_entry,
> +		.cookie = cookie,
> +	};
> +
> +	kunwind_stack_walk(arch_bpf_unwind_consume_entry, &data, current, NULL);
> +}

Too many "cookies", I found reading this confusing. If you ever respin,
please use some different "cookie" names.

I guess you want this to be merged via the bpf tree?

Acked-by: Catalin Marinas <catalin.marinas@....com>