linux-kernel - Re: [PATCH v1 2/2] LoongArch: Enable BPF exception fixup for specific ADE subcode

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Message-ID: <CAEyhmHTtEE6cnm18_WC+d+o4RnLUw+BUUNL54R6d9W2b868+LA@mail.gmail.com>
Date: Wed, 10 Dec 2025 13:20:12 +0800
From: Hengqi Chen <hengqi.chen@...il.com>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: yangtiezhu@...ngson.cn, chenhuacai@...nel.org, kernel@...0n.name, 
	zhangtianyang@...ngson.cn, masahiroy@...nel.org, linux-kernel@...r.kernel.org, 
	loongarch@...ts.linux.dev, bpf@...r.kernel.org, guodongtai@...inos.cn, 
	youling.tang@...ux.dev, jianghaoran@...inos.cn, vincent.mc.li@...il.com
Subject: Re: [PATCH v1 2/2] LoongArch: Enable BPF exception fixup for specific
 ADE subcode

On Tue, Dec 9, 2025 at 5:34 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
>
> This patch allows the LoongArch BPF JIT to handle recoverable memory
> access errors generated by BPF_PROBE_MEM* instructions.
>
> When a BPF program performs memory access operations, the instructions
> it executes may trigger ADEM exceptions. The kernel’s built-in BPF
> exception table mechanism (EX_TYPE_BPF) will generate corresponding
> exception fixup entries in the JIT compilation phase; however, the
> architecture-specific trap handling function needs to proactively call
> the common fixup routine to achieve exception recovery.
>
> do_ade(): fix EX_TYPE_BPF memory access exceptions for BPF programs,
> ensure safe execution.
>

Which bpf prog triggers this code path ? Why didn't we trigger it before ?

> Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
> ---
>  arch/loongarch/kernel/traps.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index da5926fead4a..9ca8aacc82b8 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -534,8 +534,13 @@ asmlinkage void noinstr do_fpe(struct pt_regs *regs, unsigned long fcsr)
>
>  asmlinkage void noinstr do_ade(struct pt_regs *regs)
>  {
> -       irqentry_state_t state = irqentry_enter(regs);
> +       irqentry_state_t state;
> +       unsigned int esubcode = FIELD_GET(CSR_ESTAT_ESUBCODE, regs->csr_estat);
> +
> +       if ((esubcode == 1) && fixup_exception(regs))
> +               return;
>
> +       state = irqentry_enter(regs);
>         die_if_kernel("Kernel ade access", regs);
>         force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)regs->csr_badvaddr);
>
> --
> 2.25.1
>