| Message ID | 156171315462.9468.3367572649463706996.stgit@alrua-x1 |
|---|---|
| Headers | show |
| Series | xdp: Allow lookup into devmaps before redirect | expand |
On 06/28/2019 11:12 AM, Toke Høiland-Jørgensen wrote: > When using the bpf_redirect_map() helper to redirect packets from XDP, the eBPF > program cannot currently know whether the redirect will succeed, which makes it > impossible to gracefully handle errors. To properly fix this will probably > require deeper changes to the way TX resources are allocated, but one thing that > is fairly straight forward to fix is to allow lookups into devmaps, so programs > can at least know when a redirect is *guaranteed* to fail because there is no > entry in the map. Currently, programs work around this by keeping a shadow map > of another type which indicates whether a map index is valid. > > This series contains two changes that are complementary ways to fix this issue: > > - Moving the map lookup into the bpf_redirect_map() helper (and caching the > result), so the helper can return an error if no value is found in the map. > This includes a refactoring of the devmap and cpumap code to not care about > the index on enqueue. > > - Allowing regular lookups into devmaps from eBPF programs, using the read-only > flag to make sure they don't change the values. > > The performance impact of the series is negligible, in the sense that I cannot > measure it because the variance between test runs is higher than the difference > pre/post series. > > Changelog: > > v6: > - Factor out list handling in maps to a helper in list.h (new patch 1) > - Rename variables in struct bpf_redirect_info (new patch 3 + patch 4) > - Explain why we are clearing out the map in the info struct on lookup failure > - Remove unneeded check for forwarding target in tracepoint macro > > v5: > - Rebase on latest bpf-next. > - Update documentation for bpf_redirect_map() with the new meaning of flags. > > v4: > - Fix a few nits from Andrii > - Lose the #defines in bpf.h and just compare the flags argument directly to > XDP_TX in bpf_xdp_redirect_map(). > > v3: > - Adopt Jonathan's idea of using the lower two bits of the flag value as the > return code. > - Always do the lookup, and cache the result for use in xdp_do_redirect(); to > achieve this, refactor the devmap and cpumap code to get rid the bitmap for > selecting which devices to flush. > > v2: > - For patch 1, make it clear that the change works for any map type. > - For patch 2, just use the new BPF_F_RDONLY_PROG flag to make the return > value read-only. > > --- > > Toke Høiland-Jørgensen (5): > xskmap: Move non-standard list manipulation to helper > devmap/cpumap: Use flush list instead of bitmap > devmap: Rename ifindex member in bpf_redirect_info > bpf_xdp_redirect_map: Perform map lookup in eBPF helper > devmap: Allow map lookups from eBPF > > > include/linux/filter.h | 3 + > include/linux/list.h | 14 ++++++ > include/trace/events/xdp.h | 5 +- > include/uapi/linux/bpf.h | 7 ++- > kernel/bpf/cpumap.c | 105 +++++++++++++++++++---------------------- > kernel/bpf/devmap.c | 112 ++++++++++++++++++++------------------------ > kernel/bpf/verifier.c | 7 +-- > kernel/bpf/xskmap.c | 3 - > net/core/filter.c | 60 ++++++++++++------------ > 9 files changed, 157 insertions(+), 159 deletions(-) > Applied, thanks!
When using the bpf_redirect_map() helper to redirect packets from XDP, the eBPF program cannot currently know whether the redirect will succeed, which makes it impossible to gracefully handle errors. To properly fix this will probably require deeper changes to the way TX resources are allocated, but one thing that is fairly straight forward to fix is to allow lookups into devmaps, so programs can at least know when a redirect is *guaranteed* to fail because there is no entry in the map. Currently, programs work around this by keeping a shadow map of another type which indicates whether a map index is valid. This series contains two changes that are complementary ways to fix this issue: - Moving the map lookup into the bpf_redirect_map() helper (and caching the result), so the helper can return an error if no value is found in the map. This includes a refactoring of the devmap and cpumap code to not care about the index on enqueue. - Allowing regular lookups into devmaps from eBPF programs, using the read-only flag to make sure they don't change the values. The performance impact of the series is negligible, in the sense that I cannot measure it because the variance between test runs is higher than the difference pre/post series. Changelog: v6: - Factor out list handling in maps to a helper in list.h (new patch 1) - Rename variables in struct bpf_redirect_info (new patch 3 + patch 4) - Explain why we are clearing out the map in the info struct on lookup failure - Remove unneeded check for forwarding target in tracepoint macro v5: - Rebase on latest bpf-next. - Update documentation for bpf_redirect_map() with the new meaning of flags. v4: - Fix a few nits from Andrii - Lose the #defines in bpf.h and just compare the flags argument directly to XDP_TX in bpf_xdp_redirect_map(). v3: - Adopt Jonathan's idea of using the lower two bits of the flag value as the return code. - Always do the lookup, and cache the result for use in xdp_do_redirect(); to achieve this, refactor the devmap and cpumap code to get rid the bitmap for selecting which devices to flush. v2: - For patch 1, make it clear that the change works for any map type. - For patch 2, just use the new BPF_F_RDONLY_PROG flag to make the return value read-only. --- Toke Høiland-Jørgensen (5): xskmap: Move non-standard list manipulation to helper devmap/cpumap: Use flush list instead of bitmap devmap: Rename ifindex member in bpf_redirect_info bpf_xdp_redirect_map: Perform map lookup in eBPF helper devmap: Allow map lookups from eBPF include/linux/filter.h | 3 + include/linux/list.h | 14 ++++++ include/trace/events/xdp.h | 5 +- include/uapi/linux/bpf.h | 7 ++- kernel/bpf/cpumap.c | 105 +++++++++++++++++++---------------------- kernel/bpf/devmap.c | 112 ++++++++++++++++++++------------------------ kernel/bpf/verifier.c | 7 +-- kernel/bpf/xskmap.c | 3 - net/core/filter.c | 60 ++++++++++++------------ 9 files changed, 157 insertions(+), 159 deletions(-)