Re: [PATCH v2] net: filter: BPF 'JIT' compiler for PPC64

Le mardi 19 juillet 2011 à 12:13 +1000, Matt Evans a écrit :

An implementation of a code generator for BPF programs to speed up packet
filtering on PPC64, inspired by Eric Dumazet's x86-64 version.

Filter code is generated as an ABI-compliant function in module_alloc()'d mem
with stackframe & prologue/epilogue generated if required (simple filters don't
need anything more than an li/blr).  The filter's local variables, M[], live in
registers.  Supports all BPF opcodes, although "complicated" loads from negative
packet offsets (e.g. SKF_LL_OFF) are not yet supported.

There are a couple of further optimisations left for future work; many-pass
assembly with branch-reach reduction and a register allocator to push M[]
variables into volatile registers would improve the code quality further.

This currently supports big-endian 64-bit PowerPC only (but is fairly simple
to port to PPC32 or LE!).

Enabled in the same way as x86-64:

	echo 1 > /proc/sys/net/core/bpf_jit_enable

Or, enabled with extra debug output:

	echo 2 > /proc/sys/net/core/bpf_jit_enable

Signed-off-by: Matt Evans <redacted>
---

V2: Removed some cut/paste woe in setting SEEN_X even on writes.
    Merci for le review, Eric!

 arch/powerpc/Kconfig                  |    1 +
 arch/powerpc/Makefile                 |    3 +-
 arch/powerpc/include/asm/ppc-opcode.h |   40 ++
 arch/powerpc/net/Makefile             |    4 +
 arch/powerpc/net/bpf_jit.S            |  138 +++++++
 arch/powerpc/net/bpf_jit.h            |  227 +++++++++++
 arch/powerpc/net/bpf_jit_comp.c       |  690 +++++++++++++++++++++++++++++++++
 7 files changed, 1102 insertions(+), 1 deletions(-)

+		case BPF_S_ANC_CPU:
+#ifdef CONFIG_SMP
+			/*
+			 * PACA ptr is r13:
+			 * raw_smp_processor_id() = local_paca->paca_index
+			 */

This could break if one day linux supports more than 65536 cpus :)

+			PPC_LHZ_OFFS(r_A, 13,
+				     offsetof(struct paca_struct, paca_index));
+#else
+			PPC_LI(r_A, 0);
+#endif
+			break;
+
+
+		case BPF_S_LDX_B_MSH:
+			/*
+			 * x86 version drops packet (RET 0) when K<0, whereas
+			 * interpreter does allow K<0 (__load_pointer, special
+			 * ancillary data).
+			 */

Hmm, thanks I'll take a look at this.

+			func = sk_load_byte_msh;
+			goto common_load;
+			break;
+
+			/*** Jump and branches ***/

+		default:
+			/* The filter contains something cruel & unusual.
+			 * We don't handle it, but also there shouldn't be
+			 * anything missing from our list.
+			 */
+			pr_err("BPF filter opcode %04x (@%d) unsupported\n",
+			       filter[i].code, i);

You should at least ratelimit this message ?

On x86_64 I chose to silently fall back to interpretor for a "complex
filter" or "unsupported opcode".

+			return -ENOTSUPP;
+		}
+
+	}
+	/* Set end-of-body-code address for exit. */
+	addrs[i] = ctx->idx * 4;
+
+	return 0;
+}
+