Extend ndo_bpf with two new commands used for query zero-copy support
and register an UMEM to a queue_id of a netdev.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

The xdp_umem_page holds the address for a page. Trade memory for
faster lookup. Later, we'll add DMA address here as well.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Moved struct xdp_umem to xdp_sock.h, in order to prepare for zero-copy
support.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Jesper Dangaard Brouer says:

====================
This patchset removes the net_device operation ndo_xdp_flush() call.
This is a follow merge commit ea9916ea ("Merge branch
'ndo_xdp_xmit-cleanup'").  As after commit c1ece6b2 ("bpf/xdp:
devmap can avoid calling ndo_xdp_flush") no callers of ndo_xdp_flush
are left in bpf-next tree.
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

All drivers are cleaned up and no references to ndo_xdp_flush
are left in drivers, it is time to remove the net_device_ops
operation ndo_xdp_flush.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Remove the ndo_xdp_flush call implementation tun_xdp_flush
as no callers of ndo_xdp_flush are left.

The tun drivers XDP_TX implementation also used tun_xdp_flush (and
tun_xdp_xmit).  This is easily solved by passing the XDP_XMIT_FLUSH
flag to tun_xdp_xmit in tun_xdp_tx.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Remove the ndo_xdp_flush call implementation virtnet_xdp_flush
as no callers of ndo_xdp_flush are left.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Remove the ndo_xdp_flush call implementation ixgbe_xdp_flush
as no callers of ndo_xdp_flush are left.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Remove the ndo_xdp_flush call implementation i40e_xdp_flush
as no callers of ndo_xdp_flush are left.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

The names for BPF_ALU64 | BPF_ARSH are emit_a32_arsh_*,
the names for BPF_ALU64 | BPF_LSH are emit_a32_lsh_*, but
the names for BPF_ALU64 | BPF_RSH are emit_a32_lsr_*.

For consistence reason, let's rename emit_a32_lsr_* to
emit_a32_rsh_*.

This patch also corrects a wrong comment.

Fixes: 39c13c20 ("arm: eBPF JIT compiler")
Signed-off-by: Wang YanQing <udknight@gmail.com>
Cc: Shubham Bansal <illusionist.neo@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux@armlinux.org.uk
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

imm24 is signed, so the right range is:

  [-(1<<(24 - 1)), (1<<(24 - 1)) - 1]

Note: this patch also fix a typo.

Fixes: 39c13c20 ("arm: eBPF JIT compiler")
Signed-off-by: Wang YanQing <udknight@gmail.com>
Cc: Shubham Bansal <illusionist.neo@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux@armlinux.org.uk
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Commit bf6fa2c8 ("bpf: implement bpf_get_current_cgroup_id()
helper") introduced a new helper bpf_get_current_cgroup_id().
The helper has a dependency on CONFIG_CGROUPS.

When CONFIG_CGROUPS is not defined, using the helper will result
the following verifier error:
  kernel subsystem misconfigured func bpf_get_current_cgroup_id#80
which is hard for users to interpret.
Guarding the reference to bpf_get_current_cgroup_id_proto with
CONFIG_CGROUPS will result in below better message:
  unknown func bpf_get_current_cgroup_id#80

Fixes: bf6fa2c8 ("bpf: implement bpf_get_current_cgroup_id() helper")
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Björn Töpel says:

====================
An issue with the current AF_XDP uapi raised by Mykyta Iziumtsev (see
https://www.spinics.net/lists/netdev/msg503664.html) is that it does
not support NICs that have a "type-writer" model in an efficient
way. In this model, a memory window is passed to the hardware and
multiple frames might be filled into that window, instead of just one
that we have in the current fixed frame-size model.

This patch set fixes two bugs in the current implementation and then
changes the uapi so that the type-writer model can be supported
efficiently by a possible future extension of AF_XDP.

These are the uapi changes in this patch:

* Change the "u32 idx" in the descriptors to "u64 addr". The current
  idx based format does NOT work for the type-writer model (as packets
  can start anywhere within a frame) but that a relative address
  pointer (the u64 addr) works well for both models in the prototype
  code we have that supports both models. We increased it from u32 to
  u64 to support umems larger than 4G. We have also removed the u16
  offset when having a "u64 addr" since that information is already
  carried in the least significant bits of the address.

* We want to use "u8 padding[5]" for something useful in the future
  (since we are not allowed to change its name), so we now call it
  just options so it can be extended for various purposes in the
  future. It is an u32 as that it what is left of the 16 byte
  descriptor.

* We changed the name of frame_size in the UMEM_REG setsockopt to
  chunk_size since this naming also makes sense to the type-writer
  model.

With these changes to the uapi, we believe the type-writer model can
be supported without having to resort to a new descriptor format. The
type-writer model could then be supported, from the uapi point of
view, by setting a flag at bind time and providing a new flag bit in
the options field of the descriptor that signals to user space that
all packets have been written in a chunk. Or with a new chunk
completion queue as suggested by Mykyta in his latest feedback mail on
the list.

We based this patch set on bpf-next commit bd3a08aa ("bpf:
flowlabel in bpf_fib_lookup should be flowinfo")

The structure of the patch set is as follows:

Patches 1-2: Fixes two bugs in the current implementation.
Patches 3-4: Prepares the uapi for a "type-writer" model and modifies
             the sample application so that it works with the new
	     uapi.
Patch 5: Small performance improvement patch for the sample application.

Cheers: Magnus and Björn
====================
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Here, the xdpsock sample application is adjusted to the new descriptor
format.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data.  Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).

By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.

In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.

In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.

We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.

To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.

On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.

Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.

This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Previously, rx_dropped could be updated incorrectly, e.g. if the XDP
program redirected the frame to a socket bound to a different queue
than where the XDP program was executing.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Previously the fill queue descriptor was not copied to kernel space
prior validating it, making it possible for userland to change the
descriptor post-kernel-validation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

As Michal noted the flow struct takes both the flow label and priority.
Update the bpf_fib_lookup API to note that it is flowinfo and not just
the flow label.

Cc: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Yonghong Song says:

====================
bpf has been used extensively for tracing. For example, bcc
contains an almost full set of bpf-based tools to trace kernel
and user functions/events. Most tracing tools are currently
either filtered based on pid or system-wide.

Containers have been used quite extensively in industry and
cgroup is often used together to provide resource isolation
and protection. Several processes may run inside the same
container. It is often desirable to get container-level tracing
results as well, e.g. syscall count, function count, I/O
activity, etc.

This patch implements a new helper, bpf_get_current_cgroup_id(),
which will return cgroup id based on the cgroup within which
the current task is running.

Patch #1 implements the new helper in the kernel.
Patch #2 syncs the uapi bpf.h header and helper between tools
and kernel.
Patch #3 shows how to get the same cgroup id in user space,
so a filter or policy could be configgured in the bpf program
based on current task cgroup.

Changelog:
  v1 -> v2:
     . rebase to resolve merge conflict with latest bpf-next.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Syscall name_to_handle_at() can be used to get cgroup id
for a particular cgroup path in user space. The selftest
got cgroup id from both user and kernel, and compare to
ensure they are equal to each other.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Sync kernel uapi/linux/bpf.h with tools uapi/linux/bpf.h.
Also add the necessary helper define in bpf_helpers.h.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf has been used extensively for tracing. For example, bcc
contains an almost full set of bpf-based tools to trace kernel
and user functions/events. Most tracing tools are currently
either filtered based on pid or system-wide.

Containers have been used quite extensively in industry and
cgroup is often used together to provide resource isolation
and protection. Several processes may run inside the same
container. It is often desirable to get container-level tracing
results as well, e.g. syscall count, function count, I/O
activity, etc.

This patch implements a new helper, bpf_get_current_cgroup_id(),
which will return cgroup id based on the cgroup within which
the current task is running.

The later patch will provide an example to show that
userspace can get the same cgroup id so it could
configure a filter or policy in the bpf program based on
task cgroup id.

The helper is currently implemented for tracing. It can
be added to other program types as well when needed.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Jesper Dangaard Brouer says:

====================
As I mentioned in merge commit 10f67868 ("Merge branch 'xdp_xmit-bulking'")
I plan to change the API for ndo_xdp_xmit once more, by adding a flags
argument, which is done in this patchset.

I know it is late in the cycle (currently at rc7), but it would be
nice to avoid changing NDOs over several kernel releases, as it is
annoying to vendors and distro backporters, but it is not strictly
UAPI so it is allowed (according to Alexei).

The end-goal is getting rid of the ndo_xdp_flush operation, as it will
make it possible for drivers to implement a TXQ synchronization mechanism
that is not necessarily derived from the CPU id (smp_processor_id).

This patchset removes all callers of the ndo_xdp_flush operation, but
it doesn't take the last step of removing it from all drivers.  This
can be done later, or I can update the patchset on request.

Micro-benchmarks only show a very small performance improvement, for
map-redirect around ~2 ns, and for non-map redirect ~7 ns.  I've not
benchmarked this with CONFIG_RETPOLINE, but the performance benefit
should be more visible given we end-up removing an indirect call.

---
V2: Updated based on feedback from Song Liu <songliubraving@fb.com>
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

The XDP_REDIRECT map devmap can avoid using ndo_xdp_flush, by instead
instructing ndo_xdp_xmit to flush via XDP_XMIT_FLUSH flag in
appropriate places.

Notice after this patch it is possible to remove ndo_xdp_flush
completely, as this is the last user of ndo_xdp_flush. This is left
for later patches, to keep driver changes separate.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This is the first real user of the XDP_XMIT_FLUSH flag.

As pointed out many times, XDP_REDIRECT without using BPF maps is
significant slower than the map variant.  This is primary due to the
lack of bulking, as the ndo_xdp_flush operation is required after each
frame (to avoid frames hanging on the egress device).

It is still possible to optimize this case.  Instead of invoking two
NDO indirect calls, which are very expensive with CONFIG_RETPOLINE,
instead instruct ndo_xdp_xmit to flush via XDP_XMIT_FLUSH flag.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Removing XDP_XMIT_FLAGS_NONE as all driver now implement
a flush operation in their ndo_xdp_xmit call.  The compiler
will catch if any users of XDP_XMIT_FLAGS_NONE remains.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

When passed the XDP_XMIT_FLUSH flag virtnet_xdp_xmit now performs the
same virtqueue_kick as virtnet_xdp_flush.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

When passed the XDP_XMIT_FLUSH flag tun_xdp_xmit now performs the same
kind of socket wake up as in tun_xdp_flush(). The wake up code from
tun_xdp_flush is generalized and shared with tun_xdp_xmit.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

When passed the XDP_XMIT_FLUSH flag ixgbe_xdp_xmit now performs the
same kind of ring tail update as in ixgbe_xdp_flush.  The update tail
code in ixgbe_xdp_flush is generalized and shared with ixgbe_xdp_xmit.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

When passed the XDP_XMIT_FLUSH flag i40e_xdp_xmit now performs the
same kind of ring tail update as in i40e_xdp_flush.  The advantage is
that all the necessary checks have been performed and xdp_ring can be
updated, instead of having to perform the exact same steps/checks in
i40e_xdp_flush
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This patch only change the API and reject any use of flags. This is an
intermediate step that allows us to implement the flush flag operation
later, for each individual driver in a separate patch.

The plan is to implement flush operation via XDP_XMIT_FLUSH flag
and then remove XDP_XMIT_FLAGS_NONE when done.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Daniel Borkmann says:

====================
This set adds various patches I still had in my queue, first two
are test cases to provide coverage for the recent two fixes that
went to bpf tree, then a small improvement on the error message
for gpl helpers. Next, we expose prog and map id into fdinfo in
order to allow for inspection of these objections currently used
in applications. Patch after that removes a retpoline call for
map lookup/update/delete helpers. A new helper is added in the
subsequent patch to lookup the skb's socket's cgroup v2 id which
can be used in an efficient way for e.g. lookups on egress side.
Next one is a fix to fully clear state info in tunnel/xfrm helpers.
Given this is full cap_sys_admin from init ns and has same priv
requirements like tracing, bpf-next should be okay. A small bug
fix for bpf_asm follows, and next a fix for context access in
tracing which was recently reported. Lastly, a small update in
the maintainer's file to add patchwork url and missing files.

Thanks!

v2 -> v3:
  - Noticed a merge artefact inside uapi header comment, sigh,
    fixed now.
v1 -> v2:
  - minor fix in getting context access work on 32 bit for tracing
  - add paragraph to uapi helper doc to better describe kernel
    build deps for cggroup helper
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add missing bits under tools/lib/bpf/ and also Q: entry in order to
make it easier for people to retrieve current patch queue.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Pull in recent changes from include/uapi/linux/bpf.h.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Wang reported that all the testcases for BPF_PROG_TYPE_PERF_EVENT
program type in test_verifier report the following errors on x86_32:

  172/p unpriv: spill/fill of different pointers ldx FAIL
  Unexpected error message!
  0: (bf) r6 = r10
  1: (07) r6 += -8
  2: (15) if r1 == 0x0 goto pc+3
  R1=ctx(id=0,off=0,imm=0) R6=fp-8,call_-1 R10=fp0,call_-1
  3: (bf) r2 = r10
  4: (07) r2 += -76
  5: (7b) *(u64 *)(r6 +0) = r2
  6: (55) if r1 != 0x0 goto pc+1
  R1=ctx(id=0,off=0,imm=0) R2=fp-76,call_-1 R6=fp-8,call_-1 R10=fp0,call_-1 fp-8=fp
  7: (7b) *(u64 *)(r6 +0) = r1
  8: (79) r1 = *(u64 *)(r6 +0)
  9: (79) r1 = *(u64 *)(r1 +68)
  invalid bpf_context access off=68 size=8

  378/p check bpf_perf_event_data->sample_period byte load permitted FAIL
  Failed to load prog 'Permission denied'!
  0: (b7) r0 = 0
  1: (71) r0 = *(u8 *)(r1 +68)
  invalid bpf_context access off=68 size=1

  379/p check bpf_perf_event_data->sample_period half load permitted FAIL
  Failed to load prog 'Permission denied'!
  0: (b7) r0 = 0
  1: (69) r0 = *(u16 *)(r1 +68)
  invalid bpf_context access off=68 size=2

  380/p check bpf_perf_event_data->sample_period word load permitted FAIL
  Failed to load prog 'Permission denied'!
  0: (b7) r0 = 0
  1: (61) r0 = *(u32 *)(r1 +68)
  invalid bpf_context access off=68 size=4

  381/p check bpf_perf_event_data->sample_period dword load permitted FAIL
  Failed to load prog 'Permission denied'!
  0: (b7) r0 = 0
  1: (79) r0 = *(u64 *)(r1 +68)
  invalid bpf_context access off=68 size=8

Reason is that struct pt_regs on x86_32 doesn't fully align to 8 byte
boundary due to its size of 68 bytes. Therefore, bpf_ctx_narrow_access_ok()
will then bail out saying that off & (size_default - 1) which is 68 & 7
doesn't cleanly align in the case of sample_period access from struct
bpf_perf_event_data, hence verifier wrongly thinks we might be doing an
unaligned access here though underlying arch can handle it just fine.
Therefore adjust this down to machine size and check and rewrite the
offset for narrow access on that basis. We also need to fix corresponding
pe_prog_is_valid_access(), since we hit the check for off % size != 0
(e.g. 68 % 8 -> 4) in the first and last test. With that in place, progs
for tracing work on x86_32.
Reported-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Range is 0-7, not 0-9, otherwise parser silently excludes it from the
strtol() rather than throwing an error.
Reported-by: Marc Boschma <marc@boschma.cx>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Since the remaining bits are not filled in struct bpf_tunnel_key
resp. struct bpf_xfrm_state and originate from uninitialized stack
space, we should make sure to clear them before handing control
back to the program.

Also add a padding element to struct bpf_xfrm_state for future use
similar as we have in struct bpf_tunnel_key and clear it as well.

  struct bpf_xfrm_state {
      __u32                      reqid;            /*     0     4 */
      __u32                      spi;              /*     4     4 */
      __u16                      family;           /*     8     2 */

      /* XXX 2 bytes hole, try to pack */

      union {
          __u32              remote_ipv4;          /*           4 */
          __u32              remote_ipv6[4];       /*          16 */
      };                                           /*    12    16 */

      /* size: 28, cachelines: 1, members: 4 */
      /* sum members: 26, holes: 1, sum holes: 2 */
      /* last cacheline: 28 bytes */
  };
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add a new bpf_skb_cgroup_id() helper that allows to retrieve the
cgroup id from the skb's socket. This is useful in particular to
enable bpf_get_cgroup_classid()-like behavior for cgroup v1 in
cgroup v2 by allowing ID based matching on egress. This can in
particular be used in combination with applying policy e.g. from
map lookups, and also complements the older bpf_skb_under_cgroup()
interface. In user space the cgroup id for a given path can be
retrieved through the f_handle as demonstrated in [0] recently.

  [0] https://lkml.org/lkml/2018/5/22/1190Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

While some of the BPF map lookup helpers provide a ->map_gen_lookup()
callback for inlining the map lookup altogether it is not available
for every map, so the remaining ones have to call bpf_map_lookup_elem()
helper which does a dispatch to map->ops->map_lookup_elem(). In
times of retpolines, this will control and trap speculative execution
rather than letting it do its work for the indirect call and will
therefore cause a slowdown. Likewise, bpf_map_update_elem() and
bpf_map_delete_elem() do not have an inlined version and need to call
into their map->ops->map_update_elem() resp. map->ops->map_delete_elem()
handlers.

Before:

  # bpftool prog dump xlated id 1
    0: (bf) r2 = r10
    1: (07) r2 += -8
    2: (7a) *(u64 *)(r2 +0) = 0
    3: (18) r1 = map[id:1]
    5: (85) call __htab_map_lookup_elem#232656
    6: (15) if r0 == 0x0 goto pc+4
    7: (71) r1 = *(u8 *)(r0 +35)
    8: (55) if r1 != 0x0 goto pc+1
    9: (72) *(u8 *)(r0 +35) = 1
   10: (07) r0 += 56
   11: (15) if r0 == 0x0 goto pc+4
   12: (bf) r2 = r0
   13: (18) r1 = map[id:1]
   15: (85) call bpf_map_delete_elem#215008  <-- indirect call via
   16: (95) exit                                 helper

After:

  # bpftool prog dump xlated id 1
    0: (bf) r2 = r10
    1: (07) r2 += -8
    2: (7a) *(u64 *)(r2 +0) = 0
    3: (18) r1 = map[id:1]
    5: (85) call __htab_map_lookup_elem#233328
    6: (15) if r0 == 0x0 goto pc+4
    7: (71) r1 = *(u8 *)(r0 +35)
    8: (55) if r1 != 0x0 goto pc+1
    9: (72) *(u8 *)(r0 +35) = 1
   10: (07) r0 += 56
   11: (15) if r0 == 0x0 goto pc+4
   12: (bf) r2 = r0
   13: (18) r1 = map[id:1]
   15: (85) call htab_lru_map_delete_elem#238240  <-- direct call
   16: (95) exit

In all three lookup/update/delete cases however we can use the actual
address of the map callback directly if we find that there's only a
single path with a map pointer leading to the helper call, meaning
when the map pointer has not been poisoned from verifier side.
Example code can be seen above for the delete case.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>