Re: [PATCH v4 net-next 1/3] Extended BPF interpreter and converter
From: Daniel Borkmann
Date: Tue Mar 04 2014 - 05:01:30 EST
On 03/04/2014 06:18 AM, Alexei Starovoitov wrote:
Extended BPF extends old BPF in the following ways:
- from 2 to 10 registers
Original BPF has two registers (A and X) and hidden frame pointer.
Extended BPF has ten registers and read-only frame pointer.
- from 32-bit registers to 64-bit registers
semantics of old 32-bit ALU operations are preserved via 32-bit
subregisters
- if (cond) jump_true; else jump_false;
old BPF insns are replaced with:
if (cond) jump_true; /* else fallthrough */
- adds signed > and >= insns
- 16 4-byte stack slots for register spill-fill replaced with
up to 512 bytes of multi-use stack space
- introduces bpf_call insn and register passing convention for zero
overhead calls from/to other kernel functions (not part of this patch)
- adds arithmetic right shift insn
- adds swab32/swab64 insns
- adds atomic_add insn
- old tax/txa insns are replaced with 'mov dst,src' insn
Extended BPF is designed to be JITed with one to one mapping, which
allows GCC/LLVM backends to generate optimized BPF code that performs
almost as fast as natively compiled code
sk_convert_filter() remaps old style insns into extended:
'sock_filter' instructions are remapped on the fly to
'sock_filter_ext' extended instructions when
sysctl net.core.bpf_ext_enable=1
Old filter comes through sk_attach_filter() or sk_unattached_filter_create()
if (bpf_ext_enable) {
convert to new
sk_chk_filter() - check old bpf
use sk_run_filter_ext() - new interpreter
} else {
sk_chk_filter() - check old bpf
if (bpf_jit_enable)
use old jit
else
use sk_run_filter() - old interpreter
}
sk_run_filter_ext() interpreter is noticeably faster
than sk_run_filter() for two reasons:
1.fall-through jumps
Old BPF jump instructions are forced to go either 'true' or 'false'
branch which causes branch-miss penalty.
Extended BPF jump instructions have one branch and fall-through,
which fit CPU branch predictor logic better.
'perf stat' shows drastic difference for branch-misses.
2.jump-threaded implementation of interpreter vs switch statement
Instead of single tablejump at the top of 'switch' statement, GCC will
generate multiple tablejump instructions, which helps CPU branch predictor
Performance of two BPF filters generated by libpcap was measured
on x86_64, i386 and arm32.
fprog #1 is taken from Documentation/networking/filter.txt:
tcpdump -i eth0 port 22 -dd
fprog #2 is taken from 'man tcpdump':
tcpdump -i eth0 'tcp port 22 and (((ip[2:2] - ((ip[0]&0xf)<<2)) -
((tcp[12]&0xf0)>>2)) != 0)' -dd
Other libpcap programs have similar performance differences.
Raw performance data from BPF micro-benchmark:
SK_RUN_FILTER on same SKB (cache-hit) or 10k SKBs (cache-miss)
time in nsec per call, smaller is better
--x86_64--
fprog #1 fprog #1 fprog #2 fprog #2
cache-hit cache-miss cache-hit cache-miss
old BPF 90 101 192 202
ext BPF 31 71 47 97
old BPF jit 12 34 17 44
ext BPF jit TBD
--i386--
fprog #1 fprog #1 fprog #2 fprog #2
cache-hit cache-miss cache-hit cache-miss
old BPF 107 136 227 252
ext BPF 40 119 69 172
--arm32--
fprog #1 fprog #1 fprog #2 fprog #2
cache-hit cache-miss cache-hit cache-miss
old BPF 202 300 475 540
ext BPF 139 270 296 470
old BPF jit 26 182 37 202
new BPF jit TBD
Tested with trinify BPF fuzzer
Future work:
0. seccomp
1. add extended BPF JIT for x86_64
2. add inband old/new demux and extended BPF verifier, so that new programs
can be loaded through old sk_attach_filter() and sk_unattached_filter_create()
interfaces
3. tracing filters systemtap-like with extended BPF
4. OVS with extended BPF
5. nftables with extended BPF
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Looks great, imho, some comments/questions inline:
Nit: subject line of your patches should be, e.g.
"filter: add Extended BPF interpreter and converter"
"doc: filter: add Extended BPF documentation"
...
so first "<subsystem>: <summary phrase>".
---
include/linux/filter.h | 8 +-
include/linux/netdevice.h | 1 +
include/uapi/linux/filter.h | 34 +-
net/core/filter.c | 802 ++++++++++++++++++++++++++++++++++++++++++-
net/core/sysctl_net_core.c | 7 +
5 files changed, 830 insertions(+), 22 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index e568c8ef896b..0e84ff6e991b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -52,7 +52,13 @@ extern int sk_detach_filter(struct sock *sk);
extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen);
extern int sk_get_filter(struct sock *sk, struct sock_filter __user *filter, unsigned len);
extern void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to);
+/* function remaps 'sock_filter' insns to 'sock_filter_ext' insns */
+int sk_convert_filter(struct sock_filter *old_prog, int len,
+ struct sock_filter_ext *new_prog, int *p_new_len);
+/* execute extended bpf program */
I think this and the above comment can be omitted, as both have a kernel doc
in its implementation in net/core/filter.c that is more precise.
...
+struct sock_filter_ext {
+ __u8 code; /* opcode */
+ __u8 a_reg:4; /* dest register */
+ __u8 x_reg:4; /* source register */
+ __s16 off; /* signed offset */
+ __s32 imm; /* signed immediate constant */
+};
+
struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
unsigned short len; /* Number of filter blocks */
struct sock_filter __user *filter;
@@ -45,12 +54,15 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
#define BPF_JMP 0x05
#define BPF_RET 0x06
#define BPF_MISC 0x07
+#define BPF_ALU64 0x07
+
Please do not add empty newline above.
/* ld/ldx fields */
#define BPF_SIZE(code) ((code) & 0x18)
#define BPF_W 0x00
#define BPF_H 0x08
#define BPF_B 0x10
...
diff --git a/net/core/filter.c b/net/core/filter.c
index ad30d626a5bd..1494421486b7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1,5 +1,6 @@
/*
* Linux Socket Filter - Kernel level socket filtering
+ * Extended BPF is Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
*
* Author:
* Jay Schulist <jschlst@xxxxxxxxx>
@@ -40,6 +41,8 @@
#include <linux/seccomp.h>
#include <linux/if_vlan.h>
+int bpf_ext_enable __read_mostly;
+
/* No hurry in this branch
*
* Exported for the bpf jit load helper.
@@ -399,6 +402,7 @@ load_b:
}
return 0;
+#undef K
}
EXPORT_SYMBOL(sk_run_filter);
...
+ /* RET_K, RET_A are remaped into 2 insns */
+ case BPF_RET | BPF_A:
+ case BPF_RET | BPF_K:
+ insn->code = BPF_ALU | BPF_MOV |
+ (BPF_SRC(fp->code) == BPF_K ? BPF_K : BPF_X);
Hmm, so the case statement is about BPF_RET | BPF_A and BPF_RET | BPF_K
but BPF_RET | BPF_X is not mentioned. However, in BPF_SRC(fp->code)
selection you fall back to BPF_X if it doesn't equal BPF_K? Is that
correct? And, you probably also need to handle BPF_RET | BPF_X ?
+ insn->a_reg = 0;
+ insn->x_reg = 6;
+ insn->imm = fp->k;
+
+ insn++;
+ insn->code = BPF_RET | BPF_K;
+ break;
...
+ /* RET */
+BPF_RET_BPF_K_0:
+ return regs[0/* R0 */];
--
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