2
0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-23 12:43:55 +08:00
linux-next/arch/powerpc/net
Naveen N. Rao ce0761419f powerpc/bpf: Implement support for tail calls
Tail calls allow JIT'ed eBPF programs to call into other JIT'ed eBPF
programs. This can be achieved either by:
(1) retaining the stack setup by the first eBPF program and having all
subsequent eBPF programs re-using it, or,
(2) by unwinding/tearing down the stack and having each eBPF program
deal with its own stack as it sees fit.

To ensure that this does not create loops, there is a limit to how many
tail calls can be done (currently 32). This requires the JIT'ed code to
maintain a count of the number of tail calls done so far.

Approach (1) is simple, but requires every eBPF program to have (almost)
the same prologue/epilogue, regardless of whether they need it. This is
inefficient for small eBPF programs which may not sometimes need a
prologue at all. As such, to minimize impact of tail call
implementation, we use approach (2) here which needs each eBPF program
in the chain to use its own prologue/epilogue. This is not ideal when
many tail calls are involved and when all the eBPF programs in the chain
have similar prologue/epilogue. However, the impact is restricted to
programs that do tail calls. Individual eBPF programs are not affected.

We maintain the tail call count in a fixed location on the stack and
updated tail call count values are passed in through this. The very
first eBPF program in a chain sets this up to 0 (the first 2
instructions). Subsequent tail calls skip the first two eBPF JIT
instructions to maintain the count. For programs that don't do tail
calls themselves, the first two instructions are NOPs.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2016-10-04 20:33:19 +11:00
..
bpf_jit32.h powerpc/bpf/jit: Isolate classic BPF JIT specifics into a separate header 2016-06-24 15:15:51 +10:00
bpf_jit64.h powerpc/bpf: Implement support for tail calls 2016-10-04 20:33:19 +11:00
bpf_jit_asm64.S powerpc/ebpf/jit: Implement JIT compiler for extended BPF 2016-06-24 15:17:57 +10:00
bpf_jit_asm.S powerpc/bpf/jit: Isolate classic BPF JIT specifics into a separate header 2016-06-24 15:15:51 +10:00
bpf_jit_comp64.c powerpc/bpf: Implement support for tail calls 2016-10-04 20:33:19 +11:00
bpf_jit_comp.c powerpc/bpf/jit: Isolate classic BPF JIT specifics into a separate header 2016-06-24 15:15:51 +10:00
bpf_jit.h powerpc/bpf: Implement support for tail calls 2016-10-04 20:33:19 +11:00
Makefile powerpc/ebpf/jit: Implement JIT compiler for extended BPF 2016-06-24 15:17:57 +10:00