| Message ID | 156042464138.25684.15061870566905680617.stgit@alrua-x1 |
|---|---|
| Headers | show |
| Series | xdp: Allow lookup into devmaps before redirect | expand |
On 13 Jun 2019, at 4:17, 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: > > 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. Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
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: 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 (3): devmap/cpumap: Use flush list instead of bitmap bpf_xdp_redirect_map: Perform map lookup in eBPF helper devmap: Allow map lookups from eBPF include/linux/filter.h | 1 kernel/bpf/cpumap.c | 106 +++++++++++++++++++++------------------------ kernel/bpf/devmap.c | 112 +++++++++++++++++++++++------------------------- kernel/bpf/verifier.c | 7 +-- net/core/filter.c | 29 ++++++------ 5 files changed, 118 insertions(+), 137 deletions(-)