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@xxxxxxxxxx>
> Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
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;
>
[...]
