From: Hengqi Chen <hengqi.chen@gmail.com>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Huacai Chen <chenhuacai@kernel.org>,
loongarch@lists.linux.dev, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0
Date: Sun, 15 Mar 2026 11:27:44 +0800 [thread overview]
Message-ID: <CAEyhmHQiz510vQMu-WRZ==Q71mW70UEDvyedqe8giXF=0hXSHw@mail.gmail.com> (raw)
In-Reply-To: <20260310064706.4985-1-yangtiezhu@loongson.cn>
On Tue, Mar 10, 2026 at 2:47 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> Occasionally, there exists "text_copy_cb: operation failed" when executing
> bpf selftests, the reason is copy_to_kernel_nofault() failed and the ecode
> of estat register is 0x4 (PME: Page Modification Exception) due to the pte
> is not writeable, the root cause is that there is another place to set pte
> readonly which is in the generic weak arch_protect_bpf_trampoline().
>
> There are two ways to fix this race condition issue, the direct way is to
> modify the generic weak arch_protect_bpf_trampoline() to add a mutex lock
> for set_memory_rox(), but the other simple and proper way is to just make
> arch_protect_bpf_trampoline() return 0 in the arch-specific code because
> LoongArch already uses BPF prog pack allocator for trampoline.
>
> Here are the trimmed kernel log messages:
>
> copy_to_kernel_nofault: memory access failed, ecode is 0x4
> copy_to_kernel_nofault: caller is text_copy_cb+0x50/0xa0
> text_copy_cb: operation failed
> ------------[ cut here ]------------
> bpf_prog_pack bug: missing bpf_arch_text_invalidate?
> WARNING: kernel/bpf/core.c:1008 at bpf_prog_pack_free+0x200/0x228
> ...
> Call Trace:
> [<9000000000248914>] show_stack+0x64/0x188
> [<9000000000241308>] dump_stack_lvl+0x6c/0x9c
> [<90000000002705bc>] __warn+0x9c/0x200
> [<9000000001c428c0>] __report_bug+0xa8/0x1c0
> [<9000000001c42b5c>] report_bug+0x64/0x120
> [<9000000001c7dcd0>] do_bp+0x270/0x3c0
> [<9000000000246f40>] handle_bp+0x120/0x1c0
> [<900000000047b030>] bpf_prog_pack_free+0x200/0x228
> [<900000000047b2ec>] bpf_jit_binary_pack_free+0x24/0x60
> [<900000000026989c>] bpf_jit_free+0x54/0xb0
> [<900000000029e10c>] process_one_work+0x184/0x610
> [<900000000029ef8c>] worker_thread+0x24c/0x388
> [<90000000002a902c>] kthread+0x13c/0x170
> [<9000000001c7dfe8>] ret_from_kernel_thread+0x28/0x1c0
> [<9000000000246624>] ret_from_kernel_thread_asm+0xc/0x88
>
> ---[ end trace 0000000000000000 ]---
>
> Here is a simple shell script to reproduce:
>
> #!/bin/bash
>
> for ((i=1; i<=1000; i++))
> do
> echo "under testing $i ..."
> dmesg -c > /dev/null
> ./test_progs -t fentry_attach_stress > /dev/null
> dmesg -t | grep "text_copy_cb: operation failed"
> if [ $? -eq 0 ]; then
> break
> fi
> done
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
Acked-by: Hengqi Chen <hengqi.chen@gmail.com>
> arch/loongarch/net/bpf_jit.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 3bd89f55960d..4f1af3b7a363 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -1568,6 +1568,11 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
> bpf_prog_pack_free(image, size);
> }
>
> +int arch_protect_bpf_trampoline(void *image, unsigned int size)
> +{
> + return 0;
> +}
> +
> /*
> * Sign-extend the register if necessary
> */
> --
> 2.42.0
>
next prev parent reply other threads:[~2026-03-15 3:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-10 6:47 [PATCH v1] LoongArch: BPF: Make arch_protect_bpf_trampoline() return 0 Tiezhu Yang
2026-03-10 7:29 ` bot+bpf-ci
2026-03-15 3:27 ` Hengqi Chen [this message]
2026-03-15 8:04 ` Huacai Chen
2026-03-19 21:24 ` patchwork-bot+netdevbpf
2026-03-20 3:27 ` Huacai Chen
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