Messages in this thread | | | Subject | Re: [PATCH bpf-next,v3] riscv, bpf: Add BPF exception tables | From | tongtiangen <> | Date | Thu, 28 Oct 2021 09:01:54 +0800 |
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On 2021/10/28 7:11, Daniel Borkmann wrote: > On 10/27/21 6:55 PM, Björn Töpel wrote: >> On Wed, 27 Oct 2021 at 13:03, Tong Tiangen <tongtiangen@huawei.com> 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") >>> >>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com> >>> Tested-by: Pu Lehui <pulehui@huawei.com> >>> --- >>> v3: >>> Modify according to Björn's comments, mainly code optimization. >> >> Thank you! >> >> I ran this patch against the test_bpf.ko, and selftests/bpf -- no >> regressions, and after the patch is applied more tests passes. Yay! >> >> On a related note. The RISC-V selftests/bpf is in a pretty lousy >> state. I'll send a cleanup patch for them soonish. E.g.: > > Thanks for testing! > >> * RISC-V is missing in bpf_tracing.h (libbpf) >> * Some programs don't converge in 16 steps, I had to increase it to ~32 >> * The selftest/bpf Makefile needed some RV specific changes >> * ...a lot of tests still don't pass, and needs to be looked in to > > Sounds good, please ship them. ;) > >> Feel free to add: >> >> Acked-by: Björn Töpel <bjorn@kernel.org> > > Applied, thanks! Tong, if you have a chance, please follow up with Mark's > suggestion to align the extable infra to arm64/x86.
Thanks, Mark's suggestion is good. I will improve this part if I have the opportunity. > > Thanks, > Daniel > . >
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