bpf: Reallocate BPF registers to volatile registers when possible on PPC64

Christophe Leroy Thu, 05 Aug 2021 01:21:43 -0700



Le 27/07/2021 à 08:55, Jordan Niethe a écrit :

Implement commit 40272035e1d0 ("powerpc/bpf: Reallocate BPF registers to
volatile registers when possible on PPC32") for PPC64.

When the BPF routine doesn't call any function, the non volatile
registers can be reallocated to volatile registers in order to avoid
having to save them/restore on the stack. To keep track of which
registers can be reallocated to make sure registers are set seen when
used.


Maybe you could try and do as on PPC32, try to use r0 as much as possible 
instead of TMP regs.

r0 needs to be used carefully because for some instructions (ex: addi, lwz, etc) r0 means 0 insteadof register 0, but it would help freeing one more register in several cases.


Before this patch, the test #359 ADD default X is:
    0:   nop
    4:   nop
    8:   std     r27,-40(r1)
    c:   std     r28,-32(r1)
   10:   xor     r8,r8,r8
   14:   rotlwi  r8,r8,0
   18:   xor     r28,r28,r28
   1c:   rotlwi  r28,r28,0
   20:   mr      r27,r3
   24:   li      r8,66
   28:   add     r8,r8,r28
   2c:   rotlwi  r8,r8,0
   30:   ld      r27,-40(r1)
   34:   ld      r28,-32(r1)
   38:   mr      r3,r8
   3c:   blr

After this patch, the same test has become:
    0:   nop
    4:   nop
    8:   xor     r8,r8,r8
    c:   rotlwi  r8,r8,0
   10:   xor     r5,r5,r5
   14:   rotlwi  r5,r5,0
   18:   mr      r4,r3
   1c:   li      r8,66
   20:   add     r8,r8,r5
   24:   rotlwi  r8,r8,0
   28:   mr      r3,r8
   2c:   blr

Signed-off-by: Jordan Niethe <jniet...@gmail.com>
---
  arch/powerpc/net/bpf_jit64.h      |  2 ++
  arch/powerpc/net/bpf_jit_comp64.c | 60 +++++++++++++++++++++++++------
  2 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit64.h b/arch/powerpc/net/bpf_jit64.h
index 89b625d9342b..e20521bf77bf 100644
--- a/arch/powerpc/net/bpf_jit64.h
+++ b/arch/powerpc/net/bpf_jit64.h
@@ -70,6 +70,7 @@ const int b2p[MAX_BPF_JIT_REG + 2] = {
   */
  #define PPC_BPF_LL(ctx, r, base, i) do {                                      
          \
                                if ((i) % 4) {                                  
          \
+                                       bpf_set_seen_register(ctx, 
bpf_to_ppc(ctx, TMP_REG_2));\
                                        EMIT(PPC_RAW_LI(bpf_to_ppc(ctx, 
TMP_REG_2), (i)));\
                                        EMIT(PPC_RAW_LDX(r, base,               
          \
                                                        bpf_to_ppc(ctx, 
TMP_REG_2)));     \
@@ -78,6 +79,7 @@ const int b2p[MAX_BPF_JIT_REG + 2] = {
                                } while(0)
  #define PPC_BPF_STL(ctx, r, base, i) do {                                     
          \
                                if ((i) % 4) {                                  
          \
+                                       bpf_set_seen_register(ctx, 
bpf_to_ppc(ctx, TMP_REG_2));\
                                        EMIT(PPC_RAW_LI(bpf_to_ppc(ctx, 
TMP_REG_2), (i)));\
                                        EMIT(PPC_RAW_STDX(r, base,              
          \
                                                        bpf_to_ppc(ctx, 
TMP_REG_2)));     \
diff --git a/arch/powerpc/net/bpf_jit_comp64.c 
b/arch/powerpc/net/bpf_jit_comp64.c
index f7a668c1e364..287e0322bbf3 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -66,6 +66,24 @@ static int bpf_jit_stack_offsetof(struct codegen_context 
*ctx, int reg)

void bpf_jit_realloc_regs(struct codegen_context *ctx)

  {
+       if (ctx->seen & SEEN_FUNC)
+               return;
+
+       while (ctx->seen & SEEN_NVREG_MASK &&
+              (ctx->seen & SEEN_VREG_MASK) != SEEN_VREG_MASK) {
+               int old = 32 - fls(ctx->seen & SEEN_NVREG_MASK);
+               int new = 32 - fls(~ctx->seen & SEEN_VREG_MASK);
+               int i;
+
+               for (i = BPF_REG_0; i <= TMP_REG_2; i++) {
+                       if (ctx->b2p[i] != old)
+                               continue;
+                       ctx->b2p[i] = new;
+                       bpf_set_seen_register(ctx, new);
+                       bpf_clear_seen_register(ctx, old);
+                       break;
+               }
+       }


This function is not very different from the one for PPC32. Maybe we could cook 
a common function.

void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)

@@ -106,10 +124,9 @@ void bpf_jit_build_prologue(u32 *image, struct 
codegen_context *ctx)
         * If we haven't created our own stack frame, we save these
         * in the protected zone below the previous stack frame
         */
-       for (i = BPF_REG_6; i <= BPF_REG_10; i++)
-               if (bpf_is_seen_register(ctx, bpf_to_ppc(ctx, i)))
-                       PPC_BPF_STL(ctx, bpf_to_ppc(ctx, i), 1,
-                                   bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ctx, 
i)));
+       for (i = BPF_PPC_NVR_MIN; i <= 31; i++)
+               if (bpf_is_seen_register(ctx, i))
+                       PPC_BPF_STL(ctx, i, 1, bpf_jit_stack_offsetof(ctx, i));

/* Setup frame pointer to point to the bpf stack area */

        if (bpf_is_seen_register(ctx, bpf_to_ppc(ctx, BPF_REG_FP)))
@@ -122,10 +139,9 @@ static void bpf_jit_emit_common_epilogue(u32 *image, 
struct codegen_context *ctx
        int i;

/* Restore NVRs */

-       for (i = BPF_REG_6; i <= BPF_REG_10; i++)
-               if (bpf_is_seen_register(ctx, bpf_to_ppc(ctx, i)))
-                       PPC_BPF_LL(ctx, bpf_to_ppc(ctx, i), 1,
-                                  bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ctx, 
i)));
+       for (i = BPF_PPC_NVR_MIN; i <= 31; i++)
+               if (bpf_is_seen_register(ctx, i))
+                       PPC_BPF_LL(ctx, i, 1, bpf_jit_stack_offsetof(ctx, i));

/* Tear down our stack frame */

        if (bpf_has_stack_frame(ctx)) {
@@ -223,6 +239,7 @@ static void bpf_jit_emit_tail_call(u32 *image, struct 
codegen_context *ctx, u32
         * if (index >= array->map.max_entries)
         *   goto out;
         */
+       bpf_set_seen_register(ctx, bpf_to_ppc(ctx, TMP_REG_1));
        EMIT(PPC_RAW_LWZ(bpf_to_ppc(ctx, TMP_REG_1), b2p_bpf_array,
                         offsetof(struct bpf_array, map.max_entries)));
        EMIT(PPC_RAW_RLWINM(b2p_index, b2p_index, 0, 0, 31));
@@ -318,9 +335,9 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                 * optimization but everything else should work without
                 * any issues.
                 */
-               if (dst_reg >= BPF_PPC_NVR_MIN && dst_reg < 32)
+               if (dst_reg >= 3 && dst_reg < 32)
                        bpf_set_seen_register(ctx, dst_reg);
-               if (src_reg >= BPF_PPC_NVR_MIN && src_reg < 32)
+               if (src_reg >= 3 && src_reg < 32)
                        bpf_set_seen_register(ctx, src_reg);

switch (code) {

@@ -345,6 +362,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                if (imm >= -32768 && imm < 32768)
                                        EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, 
IMM_L(imm)));
                                else {
+                                       bpf_set_seen_register(ctx, tmp1_reg);
                                        PPC_LI32(tmp1_reg, imm);
                                        EMIT(PPC_RAW_ADD(dst_reg, dst_reg, 
tmp1_reg));
                                }
@@ -362,6 +380,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        if (imm >= -32768 && imm < 32768)
                                EMIT(PPC_RAW_MULI(dst_reg, dst_reg, 
IMM_L(imm)));
                        else {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                if (BPF_CLASS(code) == BPF_ALU)
                                        EMIT(PPC_RAW_MULW(dst_reg, dst_reg, 
tmp1_reg));
@@ -372,6 +391,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_ALU | BPF_DIV | BPF_X: /* (u32) dst /= (u32) src */
                case BPF_ALU | BPF_MOD | BPF_X: /* (u32) dst %= (u32) src */
                        if (BPF_OP(code) == BPF_MOD) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                EMIT(PPC_RAW_DIVWU(tmp1_reg, dst_reg, src_reg));
                                EMIT(PPC_RAW_MULW(tmp1_reg, src_reg, tmp1_reg));
                                EMIT(PPC_RAW_SUB(dst_reg, dst_reg, tmp1_reg));
@@ -381,6 +401,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_ALU64 | BPF_DIV | BPF_X: /* dst /= src */
                case BPF_ALU64 | BPF_MOD | BPF_X: /* dst %= src */
                        if (BPF_OP(code) == BPF_MOD) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                EMIT(PPC_RAW_DIVDU(tmp1_reg, dst_reg, src_reg));
                                EMIT(PPC_RAW_MULD(tmp1_reg, src_reg, tmp1_reg));
                                EMIT(PPC_RAW_SUB(dst_reg, dst_reg, tmp1_reg));
@@ -396,10 +417,12 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        else if (imm == 1)
                                goto bpf_alu32_trunc;

+ bpf_set_seen_register(ctx, tmp1_reg);

                        PPC_LI32(tmp1_reg, imm);
                        switch (BPF_CLASS(code)) {
                        case BPF_ALU:
                                if (BPF_OP(code) == BPF_MOD) {
+                                       bpf_set_seen_register(ctx, tmp2_reg);
                                        EMIT(PPC_RAW_DIVWU(tmp2_reg, dst_reg, 
tmp1_reg));
                                        EMIT(PPC_RAW_MULW(tmp1_reg, tmp1_reg, 
tmp2_reg));
                                        EMIT(PPC_RAW_SUB(dst_reg, dst_reg, 
tmp1_reg));
@@ -408,6 +431,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                break;
                        case BPF_ALU64:
                                if (BPF_OP(code) == BPF_MOD) {
+                                       bpf_set_seen_register(ctx, tmp2_reg);
                                        EMIT(PPC_RAW_DIVDU(tmp2_reg, dst_reg, 
tmp1_reg));
                                        EMIT(PPC_RAW_MULD(tmp1_reg, tmp1_reg, 
tmp2_reg));
                                        EMIT(PPC_RAW_SUB(dst_reg, dst_reg, 
tmp1_reg));
@@ -434,6 +458,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                EMIT(PPC_RAW_ANDI(dst_reg, dst_reg, 
IMM_L(imm)));
                        else {
                                /* Sign-extended */
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                EMIT(PPC_RAW_AND(dst_reg, dst_reg, tmp1_reg));
                        }
@@ -446,6 +471,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_ALU64 | BPF_OR | BPF_K:/* dst = dst | imm */
                        if (imm < 0 && BPF_CLASS(code) == BPF_ALU64) {
                                /* Sign-extended */
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                EMIT(PPC_RAW_OR(dst_reg, dst_reg, tmp1_reg));
                        } else {
@@ -463,6 +489,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_ALU64 | BPF_XOR | BPF_K: /* dst ^= imm */
                        if (imm < 0 && BPF_CLASS(code) == BPF_ALU64) {
                                /* Sign-extended */
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                EMIT(PPC_RAW_XOR(dst_reg, dst_reg, tmp1_reg));
                        } else {
@@ -562,6 +589,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        if (BPF_SRC(code) == BPF_FROM_LE)
                                goto emit_clear;
  #endif
+                       bpf_set_seen_register(ctx, tmp1_reg);
                        switch (imm) {
                        case 16:
                                /* Rotate 8 bits left & mask with 0x0000ff00 */
@@ -625,6 +653,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_STX | BPF_MEM | BPF_B: /* *(u8 *)(dst + off) = src */
                case BPF_ST | BPF_MEM | BPF_B: /* *(u8 *)(dst + off) = imm */
                        if (BPF_CLASS(code) == BPF_ST) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                EMIT(PPC_RAW_LI(tmp1_reg, imm));
                                src_reg = tmp1_reg;
                        }
@@ -633,6 +662,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_STX | BPF_MEM | BPF_H: /* (u16 *)(dst + off) = src */
                case BPF_ST | BPF_MEM | BPF_H: /* (u16 *)(dst + off) = imm */
                        if (BPF_CLASS(code) == BPF_ST) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                EMIT(PPC_RAW_LI(tmp1_reg, imm));
                                src_reg = tmp1_reg;
                        }
@@ -641,6 +671,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_STX | BPF_MEM | BPF_W: /* *(u32 *)(dst + off) = src */
                case BPF_ST | BPF_MEM | BPF_W: /* *(u32 *)(dst + off) = imm */
                        if (BPF_CLASS(code) == BPF_ST) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                src_reg = tmp1_reg;
                        }
@@ -649,6 +680,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                case BPF_STX | BPF_MEM | BPF_DW: /* (u64 *)(dst + off) = src */
                case BPF_ST | BPF_MEM | BPF_DW: /* *(u64 *)(dst + off) = imm */
                        if (BPF_CLASS(code) == BPF_ST) {
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                PPC_LI32(tmp1_reg, imm);
                                src_reg = tmp1_reg;
                        }
@@ -669,6 +701,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        /* *(u32 *)(dst + off) += src */

/* Get EA into TMP_REG_1 */

+                       bpf_set_seen_register(ctx, tmp1_reg);
+                       bpf_set_seen_register(ctx, tmp2_reg);
                        EMIT(PPC_RAW_ADDI(tmp1_reg, dst_reg, off));
                        tmp_idx = ctx->idx * 4;
                        /* load value from memory into TMP_REG_2 */
@@ -689,6 +723,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        }
                        /* *(u64 *)(dst + off) += src */

+ bpf_set_seen_register(ctx, tmp1_reg);

+                       bpf_set_seen_register(ctx, tmp2_reg);
                        EMIT(PPC_RAW_ADDI(tmp1_reg, dst_reg, off));
                        tmp_idx = ctx->idx * 4;
                        EMIT(PPC_RAW_LDARX(tmp2_reg, 0, tmp1_reg, 0));
@@ -870,6 +906,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                break;
                        case BPF_JMP | BPF_JSET | BPF_X:
                        case BPF_JMP32 | BPF_JSET | BPF_X:
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                if (BPF_CLASS(code) == BPF_JMP) {
                                        EMIT(PPC_RAW_AND_DOT(tmp1_reg, dst_reg, 
src_reg));
                                } else {
@@ -903,6 +940,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                                EMIT(PPC_RAW_CMPLDI(dst_reg, 
imm));
                                } else {
                                        /* sign-extending load */
+                                       bpf_set_seen_register(ctx, tmp1_reg);
                                        PPC_LI32(tmp1_reg, imm);
                                        /* ... but unsigned comparison */
                                        if (is_jmp32)
@@ -933,6 +971,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                                        else
                                                EMIT(PPC_RAW_CMPDI(dst_reg, 
imm));
                                } else {
+                                       bpf_set_seen_register(ctx, tmp1_reg);
                                        PPC_LI32(tmp1_reg, imm);
                                        if (is_jmp32)
                                                EMIT(PPC_RAW_CMPW(dst_reg, 
tmp1_reg));
@@ -944,6 +983,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 
struct codegen_context *
                        case BPF_JMP | BPF_JSET | BPF_K:
                        case BPF_JMP32 | BPF_JSET | BPF_K:
                                /* andi does not sign-extend the immediate */
+                               bpf_set_seen_register(ctx, tmp1_reg);
                                if (imm >= 0 && imm < 32768)
                                        /* PPC_ANDI is _only/always_ dot-form */
                                        EMIT(PPC_RAW_ANDI(tmp1_reg, dst_reg, 
imm));

Re: [PATCH 3/3] powerpc/bpf: Reallocate BPF registers to volatile registers when possible on PPC64

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