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

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Message-ID: <9ae006cb-5081-20ce-ce29-9ba47dbede40@loongson.cn>
Date: Wed, 10 Dec 2025 09:02:16 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Chenghao Duan <duanchenghao@...inos.cn>, hengqi.chen@...il.com,
 chenhuacai@...nel.org
Cc: 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 2025/12/9 下午5:34, Chenghao Duan 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 | 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))

Please use the existing EXSUBCODE_ADEM macro definition instead of
the magic value 1.

Thanks,
Tiezhu