On Wed, Oct 27, 2021 at 11:18:22AM +0000, Tong Tiangen wrote: > When a tracing BPF program attempts to read memory without using the > bpf_probe_read() helper, the verifier marks the load instruction with > the BPF_PROBE_MEM flag. Since the riscv JIT does not currently recognize > this flag it falls back to the interpreter. > > Add support for BPF_PROBE_MEM, by appending an exception table to the > BPF program. If the load instruction causes a data abort, the fixup > infrastructure finds the exception table and fixes up the fault, by > clearing the destination register and jumping over the faulting > instruction. > > A more generic solution would add a "handler" field to the table entry, > like on x86 and s390. > > The same issue in ARM64 is fixed in: > commit 800834285361 ("bpf, arm64: Add BPF exception tables") > +#ifdef CONFIG_BPF_JIT > +int rv_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs); > +#endif > + > int fixup_exception(struct pt_regs *regs) > { > const struct exception_table_entry *fixup; > > fixup = search_exception_tables(regs->epc); > - if (fixup) { > - regs->epc = fixup->fixup; > - return 1; > - } > - return 0; > + if (!fixup) > + return 0; > + > +#ifdef CONFIG_BPF_JIT > + if (regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END) > + return rv_bpf_fixup_exception(fixup, regs); > +#endif > + > + regs->epc = fixup->fixup; > + return 1; > } As a heads-up, on the extable front, both arm64 and x86 are moving to having an enumerated "type" field to select the handler: x86: https://lore.kernel.org/lkml/20210908132525.211958725@xxxxxxxxxxxxx/ arm64: https://lore.kernel.org/linux-arm-kernel/20211019160219.5202-11-mark.rutland@xxxxxxx/ ... and going forwards, riscv might want to do likewise. Thanks, Mark.