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Commit 6651ee07 authored by Michael Holzheu's avatar Michael Holzheu Committed by David S. Miller
Browse files

s390/bpf: implement bpf_tail_call() helper 



bpf_tail_call() arguments:

 - ctx......: Context pointer
 - jmp_table: One of BPF_MAP_TYPE_PROG_ARRAY maps used as the jump table
 - index....: Index in the jump table

In this implementation s390x JIT does stack unwinding and jumps into the
callee program prologue. Caller and callee use the same stack.

With this patch a tail call generates the following code on s390x:

 if (index >= array->map.max_entries)
         goto out
 000003ff8001c7e4: e31030100016   llgf    %r1,16(%r3)
 000003ff8001c7ea: ec41001fa065   clgrj   %r4,%r1,10,3ff8001c828

 if (tail_call_cnt++ > MAX_TAIL_CALL_CNT)
         goto out;
 000003ff8001c7f0: a7080001       lhi     %r0,1
 000003ff8001c7f4: eb10f25000fa   laal    %r1,%r0,592(%r15)
 000003ff8001c7fa: ec120017207f   clij    %r1,32,2,3ff8001c828

 prog = array->prog[index];
 if (prog == NULL)
         goto out;
 000003ff8001c800: eb140003000d   sllg    %r1,%r4,3
 000003ff8001c806: e31310800004   lg      %r1,128(%r3,%r1)
 000003ff8001c80c: ec18000e007d   clgij   %r1,0,8,3ff8001c828

 Restore registers before calling function
 000003ff8001c812: eb68f2980004   lmg     %r6,%r8,664(%r15)
 000003ff8001c818: ebbff2c00004   lmg     %r11,%r15,704(%r15)

 goto *(prog->bpf_func + tail_call_start);
 000003ff8001c81e: e31100200004   lg      %r1,32(%r1,%r0)
 000003ff8001c824: 47f01006       bc      15,6(%r1)

Reviewed-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 941742f4

arch/s390/net/bpf_jit.h

+8 −2
Original line number Diff line number Diff line
@@ -28,6 +28,9 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[]; 
 *	      | old backchain |     |

 *	      +---------------+     |

 *	      |   r15 - r6    |     |

 *	      +---------------+     |

 *	      | 4 byte align  |     |

 *	      | tail_call_cnt |     |

 * BFP	   -> +===============+     |

 *	      |		      |     |

 *	      |   BPF stack   |     |
@@ -46,14 +49,17 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[]; 
 * R15	   -> +---------------+     + low

 *

 * We get 160 bytes stack space from calling function, but only use

 * 11 * 8 byte (old backchain + r15 - r6) for storing registers.

 * 12 * 8 byte for old backchain, r15..r6, and tail_call_cnt.

 */

#define STK_SPACE	(MAX_BPF_STACK + 8 + 4 + 4 + 160)

#define STK_160_UNUSED	(160 - 11 * 8)

#define STK_160_UNUSED	(160 - 12 * 8)

#define STK_OFF		(STK_SPACE - STK_160_UNUSED)

#define STK_OFF_TMP	160	/* Offset of tmp buffer on stack */

#define STK_OFF_HLEN	168	/* Offset of SKB header length on stack */



#define STK_OFF_R6	(160 - 11 * 8)	/* Offset of r6 on stack */

#define STK_OFF_TCCNT	(160 - 12 * 8)	/* Offset of tail_call_cnt on stack */



/* Offset to skip condition code check */

#define OFF_OK		4

arch/s390/net/bpf_jit_comp.c

+104 −2
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
#include <linux/netdevice.h>

#include <linux/filter.h>

#include <linux/init.h>

#include <linux/bpf.h>

#include <asm/cacheflush.h>

#include <asm/dis.h>

#include "bpf_jit.h"
@@ -40,6 +41,8 @@ struct bpf_jit { 
	int base_ip;		/* Base address for literal pool */

	int ret0_ip;		/* Address of return 0 */

	int exit_ip;		/* Address of exit */

	int tail_call_start;	/* Tail call start offset */

	int labels[1];		/* Labels for local jumps */

};



#define BPF_SIZE_MAX	4096	/* Max size for program */
@@ -49,6 +52,7 @@ struct bpf_jit { 
#define SEEN_RET0	4	/* ret0_ip points to a valid return 0 */

#define SEEN_LITERAL	8	/* code uses literals */

#define SEEN_FUNC	16	/* calls C functions */

#define SEEN_TAIL_CALL	32	/* code uses tail calls */

#define SEEN_STACK	(SEEN_FUNC | SEEN_MEM | SEEN_SKB)



/*
@@ -60,6 +64,7 @@ struct bpf_jit { 
#define REG_L		(__MAX_BPF_REG+3)	/* Literal pool register */

#define REG_15		(__MAX_BPF_REG+4)	/* Register 15 */

#define REG_0		REG_W0			/* Register 0 */

#define REG_1		REG_W1			/* Register 1 */

#define REG_2		BPF_REG_1		/* Register 2 */

#define REG_14		BPF_REG_0		/* Register 14 */
@@ -223,6 +228,24 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1) 
	REG_SET_SEEN(b3);					\

})



#define EMIT6_PCREL_LABEL(op1, op2, b1, b2, label, mask)	\

({								\

	int rel = (jit->labels[label] - jit->prg) >> 1;		\

	_EMIT6(op1 | reg(b1, b2) << 16 | (rel & 0xffff),	\

	       op2 | mask << 12);				\

	REG_SET_SEEN(b1);					\

	REG_SET_SEEN(b2);					\

})



#define EMIT6_PCREL_IMM_LABEL(op1, op2, b1, imm, label, mask)	\

({								\

	int rel = (jit->labels[label] - jit->prg) >> 1;		\

	_EMIT6(op1 | (reg_high(b1) | mask) << 16 |		\

		(rel & 0xffff), op2 | (imm & 0xff) << 8);	\

	REG_SET_SEEN(b1);					\

	BUILD_BUG_ON(((unsigned long) imm) > 0xff);		\

})



#define EMIT6_PCREL(op1, op2, b1, b2, i, off, mask)		\

({								\

	/* Branch instruction needs 6 bytes */			\
@@ -286,7 +309,7 @@ static void jit_fill_hole(void *area, unsigned int size) 
 */

static void save_regs(struct bpf_jit *jit, u32 rs, u32 re)

{

	u32 off = 72 + (rs - 6) * 8;

	u32 off = STK_OFF_R6 + (rs - 6) * 8;



	if (rs == re)

		/* stg %rs,off(%r15) */
@@ -301,7 +324,7 @@ static void save_regs(struct bpf_jit *jit, u32 rs, u32 re) 
 */

static void restore_regs(struct bpf_jit *jit, u32 rs, u32 re)

{

	u32 off = 72 + (rs - 6) * 8;

	u32 off = STK_OFF_R6 + (rs - 6) * 8;



	if (jit->seen & SEEN_STACK)

		off += STK_OFF;
@@ -374,6 +397,16 @@ static void save_restore_regs(struct bpf_jit *jit, int op) 
 */

static void bpf_jit_prologue(struct bpf_jit *jit)

{

	if (jit->seen & SEEN_TAIL_CALL) {

		/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */

		_EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT);

	} else {

		/* j tail_call_start: NOP if no tail calls are used */

		EMIT4_PCREL(0xa7f40000, 6);

		_EMIT2(0);

	}

	/* Tail calls have to skip above initialization */

	jit->tail_call_start = jit->prg;

	/* Save registers */

	save_restore_regs(jit, REGS_SAVE);

	/* Setup literal pool */
@@ -951,6 +984,75 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i 
		EMIT4(0xb9040000, BPF_REG_0, REG_2);

		break;

	}

	case BPF_JMP | BPF_CALL | BPF_X:

		/*

		 * Implicit input:

		 *  B1: pointer to ctx

		 *  B2: pointer to bpf_array

		 *  B3: index in bpf_array

		 */

		jit->seen |= SEEN_TAIL_CALL;



		/*

		 * if (index >= array->map.max_entries)

		 *         goto out;

		 */



		/* llgf %w1,map.max_entries(%b2) */

		EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_2,

			      offsetof(struct bpf_array, map.max_entries));

		/* clgrj %b3,%w1,0xa,label0: if %b3 >= %w1 goto out */

		EMIT6_PCREL_LABEL(0xec000000, 0x0065, BPF_REG_3,

				  REG_W1, 0, 0xa);



		/*

		 * if (tail_call_cnt++ > MAX_TAIL_CALL_CNT)

		 *         goto out;

		 */



		if (jit->seen & SEEN_STACK)

			off = STK_OFF_TCCNT + STK_OFF;

		else

			off = STK_OFF_TCCNT;

		/* lhi %w0,1 */

		EMIT4_IMM(0xa7080000, REG_W0, 1);

		/* laal %w1,%w0,off(%r15) */

		EMIT6_DISP_LH(0xeb000000, 0x00fa, REG_W1, REG_W0, REG_15, off);

		/* clij %w1,MAX_TAIL_CALL_CNT,0x2,label0 */

		EMIT6_PCREL_IMM_LABEL(0xec000000, 0x007f, REG_W1,

				      MAX_TAIL_CALL_CNT, 0, 0x2);



		/*

		 * prog = array->prog[index];

		 * if (prog == NULL)

		 *         goto out;

		 */



		/* sllg %r1,%b3,3: %r1 = index * 8 */

		EMIT6_DISP_LH(0xeb000000, 0x000d, REG_1, BPF_REG_3, REG_0, 3);

		/* lg %r1,prog(%b2,%r1) */

		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, BPF_REG_2,

			      REG_1, offsetof(struct bpf_array, prog));

		/* clgij %r1,0,0x8,label0 */

		EMIT6_PCREL_IMM_LABEL(0xec000000, 0x007d, REG_1, 0, 0, 0x8);



		/*

		 * Restore registers before calling function

		 */

		save_restore_regs(jit, REGS_RESTORE);



		/*

		 * goto *(prog->bpf_func + tail_call_start);

		 */



		/* lg %r1,bpf_func(%r1) */

		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, REG_1, REG_0,

			      offsetof(struct bpf_prog, bpf_func));

		/* bc 0xf,tail_call_start(%r1) */

		_EMIT4(0x47f01000 + jit->tail_call_start);

		/* out: */

		jit->labels[0] = jit->prg;

		break;

	case BPF_JMP | BPF_EXIT: /* return b0 */

		last = (i == fp->len - 1) ? 1 : 0;

		if (last && !(jit->seen & SEEN_RET0))