linux-kernel - Re: [PATCH bpf] bpf: fix UML x86

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Date: Thu, 13 Jun 2024 23:30:42 +0800
From: Shung-Hsi Yu <shung-hsi.yu@...e.com>
To: Maciej Żenczykowski <maze@...gle.com>
Cc: Maciej Żenczykowski <zenczykowski@...il.com>, 
	Linux Network Development Mailing List <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	BPF Mailing List <bpf@...r.kernel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH bpf] bpf: fix UML x86_64 compile failure

On Thu, Jun 13, 2024 at 04:25:20AM GMT, Maciej Żenczykowski wrote:
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper")
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
> ---
>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 36ef8e96787e..7a354b1e6197 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20313,7 +20313,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  			goto next_insn;
>  		}
>  
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
>  		/* Implement bpf_get_smp_processor_id() inline. */
>  		if (insn->imm == BPF_FUNC_get_smp_processor_id &&
>  		    prog->jit_requested && bpf_jit_supports_percpu_insn()) {

The patch needs a change description[1].

Maybe something along the line of why pcpu_hot.cpu_number not accessible
in User-mode Linux? (I don't know bpf_get_smp_processor_id() or UML that
well, just suggesting possible change description)

1: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes