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Date: Thu, 28 Oct 2021 01:11:03 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Björn Töpel <bjorn.topel@...il.com>, Tong Tiangen <tongtiangen@...wei.com> Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Palmer Dabbelt <palmerdabbelt@...gle.com>, Albert Ou <aou@...s.berkeley.edu>, Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>, Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, linux-riscv <linux-riscv@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org> Subject: Re: [PATCH bpf-next,v3] riscv, bpf: Add BPF exception tables On 10/27/21 6:55 PM, Björn Töpel wrote: > On Wed, 27 Oct 2021 at 13:03, Tong Tiangen <tongtiangen@...wei.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@...wei.com> >> Tested-by: Pu Lehui <pulehui@...wei.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@...nel.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, Daniel
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