MIPS: BPF: Introduce BPF ASM helpers

This commit introduces BPF ASM helpers for MIPS and MIPS64 kernels.
The purpose of this patch is to twofold:

1) We are now able to handle negative offsets instead of either
falling back to the interpreter or to simply not do anything and
bail out.

2) Optimize reads from the packet header instead of calling the C
helpers

Because of this patch, we are now able to get rid of quite a bit of
code in the JIT generation process by using MIPS optimized assembly
code. The new assembly code makes the test_bpf testsuite happy with
all 60 test passing successfully compared to the previous
implementation where 2 tests were failing.
Doing some basic analysis in the results between the old
implementation and the new one we can obtain the following
summary running current mainline on an ER8 board (+/- 30us delta is
ignored to prevent noise from kernel scheduling or IRQ latencies):

Summary: 22 tests are faster, 7 are slower and 47 saw no improvement

with the most notable improvement being the tcpdump tests. The 7 tests
that seem to be a bit slower is because they all follow the slow path
(bpf_internal_load_pointer_neg_helper) which is meant to be slow so
that's not a problem.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: netdev@vger.kernel.org
Patchwork: http://patchwork.linux-mips.org/patch/10530/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 18 insertions, 15 deletions

diff --git a/arch/mips/net/bpf_jit.h b/arch/mips/net/bpf_jit.h
index 3afa7a6d81b3..8f9f54841123 100644
--- a/arch/mips/net/bpf_jit.h
+++ b/arch/mips/net/bpf_jit.h
@@ -15,7 +15,6 @@
 /* Registers used by JIT */
 #define MIPS_R_ZERO	0
 #define MIPS_R_V0	2
-#define MIPS_R_V1	3
 #define MIPS_R_A0	4
 #define MIPS_R_A1	5
 #define MIPS_R_T4	12
@@ -43,20 +42,6 @@
 #define MIPS_COND_X	(0x1 << 5)
 #define MIPS_COND_K	(0x1 << 6)
 
-/* ABI specific return values */
-#ifdef CONFIG_32BIT /* O32 */
-#ifdef CONFIG_CPU_LITTLE_ENDIAN
-#define r_err	MIPS_R_V1
-#define r_val	MIPS_R_V0
-#else /* CONFIG_CPU_LITTLE_ENDIAN */
-#define r_err	MIPS_R_V0
-#define r_val	MIPS_R_V1
-#endif
-#else /* N64 */
-#define r_err	MIPS_R_V0
-#define r_val	MIPS_R_V0
-#endif
-
 #define r_ret	MIPS_R_V0
 
 /*
@@ -65,11 +50,14 @@
  * any of the $s0-$s6 registers will only be preserved if
  * they are going to actually be used.
  */
+#define r_skb_hl	MIPS_R_S0 /* skb header length */
+#define r_skb_data	MIPS_R_S1 /* skb actual data */
 #define r_off		MIPS_R_S2
 #define r_A		MIPS_R_S3
 #define r_X		MIPS_R_S4
 #define r_skb		MIPS_R_S5
 #define r_M		MIPS_R_S6
+#define r_skb_len	MIPS_R_S7
 #define r_s0		MIPS_R_T4 /* scratch reg 1 */
 #define r_s1		MIPS_R_T5 /* scratch reg 2 */
 #define r_tmp_imm	MIPS_R_T6 /* No need to preserve this */
@@ -78,4 +66,19 @@
 #define r_sp		MIPS_R_SP
 #define r_ra		MIPS_R_RA
 
+#ifndef __ASSEMBLY__
+
+/* Declare ASM helpers */
+
+#define DECLARE_LOAD_FUNC(func) \
+	extern u8 func(unsigned long *skb, int offset); \
+	extern u8 func##_negative(unsigned long *skb, int offset); \
+	extern u8 func##_positive(unsigned long *skb, int offset)
+
+DECLARE_LOAD_FUNC(sk_load_word);
+DECLARE_LOAD_FUNC(sk_load_half);
+DECLARE_LOAD_FUNC(sk_load_byte);
+
+#endif
+
 #endif /* BPF_JIT_MIPS_OP_H */