diff options
author | Alexei Starovoitov <ast@plumgrid.com> | 2015-07-21 06:34:18 +0300 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2015-07-21 06:52:31 +0300 |
commit | 4e10df9a60d96ced321dd2af71da558c6b750078 (patch) | |
tree | 6a913ab31a28d48de3b3510470320220eb75e6eb /arch/x86/net | |
parent | f3120acc7851bffd1cd15acd044b7fa6fa520e75 (diff) | |
download | linux-4e10df9a60d96ced321dd2af71da558c6b750078.tar.xz |
bpf: introduce bpf_skb_vlan_push/pop() helpers
Allow eBPF programs attached to TC qdiscs call skb_vlan_push/pop via
helper functions. These functions may change skb->data/hlen which are
cached by some JITs to improve performance of ld_abs/ld_ind instructions.
Therefore JITs need to recognize bpf_skb_vlan_push/pop() calls,
re-compute header len and re-cache skb->data/hlen back into cpu registers.
Note, skb->data/hlen are not directly accessible from the programs,
so any changes to skb->data done either by these helpers or by other
TC actions are safe.
eBPF JIT supported by three architectures:
- arm64 JIT is using bpf_load_pointer() without caching, so it's ok as-is.
- x64 JIT re-caches skb->data/hlen unconditionally after vlan_push/pop calls
(experiments showed that conditional re-caching is slower).
- s390 JIT falls back to interpreter for now when bpf_skb_vlan_push() is present
in the program (re-caching is tbd).
These helpers allow more scalable handling of vlan from the programs.
Instead of creating thousands of vlan netdevs on top of eth0 and attaching
TC+ingress+bpf to all of them, the program can be attached to eth0 directly
and manipulate vlans as necessary.
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch/x86/net')
-rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 80 |
1 files changed, 42 insertions, 38 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 579a8fd74be0..6c335a8fc086 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -315,6 +315,26 @@ static void emit_bpf_tail_call(u8 **pprog) *pprog = prog; } + +static void emit_load_skb_data_hlen(u8 **pprog) +{ + u8 *prog = *pprog; + int cnt = 0; + + /* r9d = skb->len - skb->data_len (headlen) + * r10 = skb->data + */ + /* mov %r9d, off32(%rdi) */ + EMIT3_off32(0x44, 0x8b, 0x8f, offsetof(struct sk_buff, len)); + + /* sub %r9d, off32(%rdi) */ + EMIT3_off32(0x44, 0x2b, 0x8f, offsetof(struct sk_buff, data_len)); + + /* mov %r10, off32(%rdi) */ + EMIT3_off32(0x4c, 0x8b, 0x97, offsetof(struct sk_buff, data)); + *pprog = prog; +} + static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, int oldproglen, struct jit_context *ctx) { @@ -329,36 +349,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, emit_prologue(&prog); - if (seen_ld_abs) { - /* r9d : skb->len - skb->data_len (headlen) - * r10 : skb->data - */ - if (is_imm8(offsetof(struct sk_buff, len))) - /* mov %r9d, off8(%rdi) */ - EMIT4(0x44, 0x8b, 0x4f, - offsetof(struct sk_buff, len)); - else - /* mov %r9d, off32(%rdi) */ - EMIT3_off32(0x44, 0x8b, 0x8f, - offsetof(struct sk_buff, len)); - - if (is_imm8(offsetof(struct sk_buff, data_len))) - /* sub %r9d, off8(%rdi) */ - EMIT4(0x44, 0x2b, 0x4f, - offsetof(struct sk_buff, data_len)); - else - EMIT3_off32(0x44, 0x2b, 0x8f, - offsetof(struct sk_buff, data_len)); - - if (is_imm8(offsetof(struct sk_buff, data))) - /* mov %r10, off8(%rdi) */ - EMIT4(0x4c, 0x8b, 0x57, - offsetof(struct sk_buff, data)); - else - /* mov %r10, off32(%rdi) */ - EMIT3_off32(0x4c, 0x8b, 0x97, - offsetof(struct sk_buff, data)); - } + if (seen_ld_abs) + emit_load_skb_data_hlen(&prog); for (i = 0; i < insn_cnt; i++, insn++) { const s32 imm32 = insn->imm; @@ -367,6 +359,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 b1 = 0, b2 = 0, b3 = 0; s64 jmp_offset; u8 jmp_cond; + bool reload_skb_data; int ilen; u8 *func; @@ -818,12 +811,18 @@ xadd: if (is_imm8(insn->off)) func = (u8 *) __bpf_call_base + imm32; jmp_offset = func - (image + addrs[i]); if (seen_ld_abs) { - EMIT2(0x41, 0x52); /* push %r10 */ - EMIT2(0x41, 0x51); /* push %r9 */ - /* need to adjust jmp offset, since - * pop %r9, pop %r10 take 4 bytes after call insn - */ - jmp_offset += 4; + reload_skb_data = bpf_helper_changes_skb_data(func); + if (reload_skb_data) { + EMIT1(0x57); /* push %rdi */ + jmp_offset += 22; /* pop, mov, sub, mov */ + } else { + EMIT2(0x41, 0x52); /* push %r10 */ + EMIT2(0x41, 0x51); /* push %r9 */ + /* need to adjust jmp offset, since + * pop %r9, pop %r10 take 4 bytes after call insn + */ + jmp_offset += 4; + } } if (!imm32 || !is_simm32(jmp_offset)) { pr_err("unsupported bpf func %d addr %p image %p\n", @@ -832,8 +831,13 @@ xadd: if (is_imm8(insn->off)) } EMIT1_off32(0xE8, jmp_offset); if (seen_ld_abs) { - EMIT2(0x41, 0x59); /* pop %r9 */ - EMIT2(0x41, 0x5A); /* pop %r10 */ + if (reload_skb_data) { + EMIT1(0x5F); /* pop %rdi */ + emit_load_skb_data_hlen(&prog); + } else { + EMIT2(0x41, 0x59); /* pop %r9 */ + EMIT2(0x41, 0x5A); /* pop %r10 */ + } } break; |