linux-kernel - Re: [PATCH v2 4/4] LoongArch: BPF: Enable BPF exception fixup for specific ADE subcode

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Message-ID: <CAAhV-H5-AaD9SuRWt5gK4ODVA356EO7byqf-AnXvr_0C+FuUPg@mail.gmail.com>
Date: Sat, 13 Dec 2025 21:16:00 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: yangtiezhu@...ngson.cn, hengqi.chen@...il.com, kernel@...0n.name, 
	zhangtianyang@...ngson.cn, masahiroy@...nel.org, linux-kernel@...r.kernel.org, 
	loongarch@...ts.linux.dev, bpf@...r.kernel.org, youling.tang@...ux.dev, 
	jianghaoran@...inos.cn, vincent.mc.li@...il.com
Subject: Re: [PATCH v2 4/4] LoongArch: BPF: Enable BPF exception fixup for
 specific ADE subcode

Hi, Chenghao,

On Fri, Dec 12, 2025 at 5:11 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.
>
> Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
> ---
>  arch/loongarch/kernel/traps.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index da5926fead4a..4cf72e0af6a3 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -534,7 +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 == EXSUBCODE_ADEM) && fixup_exception(regs))
> +               return;
No chance for ADEF? And I don't think ixup_exception() can be done out
of irqentry_enter().

This patch is needed by BPF but not part of BPF, so I think the
subject should be:
LoongArch: Enable exception fixup for specific ADE subcode

Huacai

> +
> +       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
>