From: Eduard Zingerman <eddyz87@gmail.com>
To: Puranjay Mohan <puranjay@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
Xu Kuohai <xukuohai@huaweicloud.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v5 3/4] bpf: Report arena faults to BPF stderr
Date: Tue, 02 Sep 2025 17:01:35 -0700 [thread overview]
Message-ID: <f41d83899f6d2dda1b55fe7f91f0816b9e23361a.camel@gmail.com> (raw)
In-Reply-To: <20250901193730.43543-4-puranjay@kernel.org>
On Mon, 2025-09-01 at 19:37 +0000, Puranjay Mohan wrote:
> Begin reporting arena page faults and the faulting address to BPF
> program's stderr, this patch adds support in the arm64 and x86-64 JITs,
> support for other archs can be added later.
>
> The fault handlers receive the 32 bit address in the arena region so
> the upper 32 bits of user_vm_start is added to it before printing the
> address. This is what the user would expect to see as this is what is
> printed by bpf_printk() is you pass it an address returned by
> bpf_arena_alloc_pages();
>
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>
> ---
Fwiw, aside from a nit below the patch looks good to me.
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 7e3fca1646203..644424ae5e5d2 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
[...]
> @@ -2089,8 +2143,25 @@ st: if (is_imm8(insn->off))
>
> ex->data = EX_TYPE_BPF;
>
> - ex->fixup = (prog - start_of_ldx) |
> - ((BPF_CLASS(insn->code) == BPF_LDX ? reg2pt_regs[dst_reg] : DONT_CLEAR) << 8);
> + is_arena = (BPF_MODE(insn->code) == BPF_PROBE_MEM32) ||
> + (BPF_MODE(insn->code) == BPF_PROBE_ATOMIC);
Nit:
It looks like label `populate_extable` is always reachable from either
BPF_PROB_MEM32 or BPF_PROBE_ATOMIC instruction. Non-arena use cases
for BPF_PROBE_MEM{,SX} are handled separately. So, it appears that
this condition is always true.
> +
> + fixup_reg = (BPF_CLASS(insn->code) == BPF_LDX) ?
> + reg2pt_regs[dst_reg] : DONT_CLEAR;
> +
> + ex->fixup = FIELD_PREP(FIXUP_INSN_LEN_MASK, prog - start_of_ldx) |
> + FIELD_PREP(FIXUP_REG_MASK, fixup_reg);
> +
> + if (is_arena) {
> + ex->fixup |= FIXUP_ARENA_ACCESS;
> + if (BPF_CLASS(insn->code) == BPF_LDX)
> + arena_reg = reg2pt_regs[src_reg];
> + else
> + arena_reg = reg2pt_regs[dst_reg];
> +
> + ex->fixup |= FIELD_PREP(FIXUP_ARENA_REG_MASK, arena_reg);
> + ex->data |= FIELD_PREP(DATA_ARENA_OFFSET_MASK, insn->off);
> + }
> }
> break;
>
[...]
next prev parent reply other threads:[~2025-09-03 0:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-01 19:37 [PATCH bpf-next v5 0/4] bpf: report arena faults to BPF streams Puranjay Mohan
2025-09-01 19:37 ` [PATCH bpf-next v5 1/4] bpf: arm64: simplify exception table handling Puranjay Mohan
2025-09-01 19:37 ` [PATCH bpf-next v5 2/4] bpf: core: introduce main_prog_aux for stream access Puranjay Mohan
2025-09-02 2:25 ` Alexei Starovoitov
2025-09-02 2:32 ` Kumar Kartikeya Dwivedi
2025-09-01 19:37 ` [PATCH bpf-next v5 3/4] bpf: Report arena faults to BPF stderr Puranjay Mohan
2025-09-02 12:42 ` kernel test robot
2025-09-03 0:01 ` Eduard Zingerman [this message]
2025-09-01 19:37 ` [PATCH bpf-next v5 4/4] selftests/bpf: Add tests for arena fault reporting Puranjay Mohan
2025-09-02 16:22 ` Yonghong Song
2025-09-02 22:21 ` Eduard Zingerman
2025-09-05 14:00 ` Puranjay Mohan
2025-09-05 18:38 ` Eduard Zingerman
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