4.17-stable review patch. If anyone has any objections, please let me know.
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From: Jakub Kicinski jakub.kicinski@netronome.com
[ Upstream commit 68d676a089625daed9d61df56ac63b5cd7189efe ]
Stopping offload completely if replace of program failed dates back to days of transparent offload. Back then we wanted to silently fall back to the in-driver processing. Today we mark programs for offload when they are loaded into the kernel, so the transparent offload is no longer a reality.
Flags check in the driver will only allow replace of a driver program with another driver program or an offload program with another offload program.
When driver program is replaced stopping offload is a no-op, because driver program isn't offloaded. When replacing offloaded program if the offload fails the entire operation will fail all the way back to user space and we should continue using the old program. IOW when replacing a driver program stopping offload is unnecessary and when replacing offloaded program - it's a bug, old program should continue to run.
In practice this bug would mean that if offload operation was to fail (either due to FW communication error, kernel OOM or new program being offloaded but for a different netdev) driver would continue reporting that previous XDP program is offloaded but in fact no program will be loaded in hardware. The failure is fairly unlikely (found by inspection, when working on the code) but it's unpleasant.
Backport note: even though the bug was introduced in commit cafa92ac2553 ("nfp: bpf: add support for XDP_FLAGS_HW_MODE"), this fix depends on commit 441a33031fe5 ("net: xdp: don't allow device-bound programs in driver mode"), so this fix is sufficient only in v4.15 or newer. Kernels v4.13.x and v4.14.x do need to stop offload if it was transparent/opportunistic, i.e. if XDP_FLAGS_HW_MODE was not set on running program.
Fixes: cafa92ac2553 ("nfp: bpf: add support for XDP_FLAGS_HW_MODE") Signed-off-by: Jakub Kicinski jakub.kicinski@netronome.com Reviewed-by: Quentin Monnet quentin.monnet@netronome.com Acked-by: Song Liu songliubraving@fb.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/netronome/nfp/bpf/main.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/drivers/net/ethernet/netronome/nfp/bpf/main.c +++ b/drivers/net/ethernet/netronome/nfp/bpf/main.c @@ -73,10 +73,10 @@ nfp_bpf_xdp_offload(struct nfp_app *app,
ret = nfp_net_bpf_offload(nn, prog, running, extack); /* Stop offload if replace not possible */ - if (ret && prog) - nfp_bpf_xdp_offload(app, nn, NULL, extack); + if (ret) + return ret;
- nn->dp.bpf_offload_xdp = prog && !ret; + nn->dp.bpf_offload_xdp = !!prog; return ret; }