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bpf: powerpc64: optimize JIT passes for bpf function calls

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Once the JITed images for each function in a multi-function program
are generated after the first three JIT passes, we only need to fix
the target address for the branch instruction corresponding to each
bpf-to-bpf function call.

This introduces the following optimizations for reducing the work
done by the JIT compiler when handling multi-function programs:

  [1] Instead of doing two extra passes to fix the bpf function calls,
      do just one as that would be sufficient.

  [2] During the extra pass, only overwrite the instruction sequences
      for the bpf-to-bpf function calls as everything else would still
      remain exactly the same. This also reduces the number of writes
      to the JITed image.

  [3] Do not regenerate the prologue and the epilogue during the extra
      pass as that would be redundant.

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Sandipan Das 2018-12-03 17:51:04 +05:30 committed by Daniel Borkmann
parent dcb40590e6
commit 025dceb0fa
1 changed files with 66 additions and 0 deletions
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66
arch/powerpc/net/bpf_jit_comp64.c
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@ -891,6 +891,55 @@ cond_branch:
return 0;
}
/* Fix the branch target addresses for subprog calls */
static int bpf_jit_fixup_subprog_calls(struct bpf_prog *fp, u32 *image,
struct codegen_context *ctx, u32 *addrs)
{
const struct bpf_insn *insn = fp->insnsi;
bool func_addr_fixed;
u64 func_addr;
u32 tmp_idx;
int i, ret;
for (i = 0; i < fp->len; i++) {
/*
* During the extra pass, only the branch target addresses for
* the subprog calls need to be fixed. All other instructions
* can left untouched.
*
* The JITed image length does not change because we already
* ensure that the JITed instruction sequence for these calls
* are of fixed length by padding them with NOPs.
*/
if (insn[i].code == (BPF_JMP | BPF_CALL) &&
insn[i].src_reg == BPF_PSEUDO_CALL) {
ret = bpf_jit_get_func_addr(fp, &insn[i], true,
&func_addr,
&func_addr_fixed);
if (ret < 0)
return ret;
/*
* Save ctx->idx as this would currently point to the
* end of the JITed image and set it to the offset of
* the instruction sequence corresponding to the
* subprog call temporarily.
*/
tmp_idx = ctx->idx;
ctx->idx = addrs[i] / 4;
bpf_jit_emit_func_call_rel(image, ctx, func_addr);
/*
* Restore ctx->idx here. This is safe as the length
* of the JITed sequence remains unchanged.
*/
ctx->idx = tmp_idx;
}
}
return 0;
}
struct powerpc64_jit_data {
struct bpf_binary_header *header;
u32 *addrs;
@ -989,6 +1038,22 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
skip_init_ctx:
code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
if (extra_pass) {
/*
* Do not touch the prologue and epilogue as they will remain
* unchanged. Only fix the branch target address for subprog
* calls in the body.
*
* This does not change the offsets and lengths of the subprog
* call instruction sequences and hence, the size of the JITed
* image as well.
*/
bpf_jit_fixup_subprog_calls(fp, code_base, &cgctx, addrs);
/* There is no need to perform the usual passes. */
goto skip_codegen_passes;
}
/* Code generation passes 1-2 */
for (pass = 1; pass < 3; pass++) {
/* Now build the prologue, body code & epilogue for real. */
@ -1002,6 +1067,7 @@ skip_init_ctx:
proglen - (cgctx.idx * 4), cgctx.seen);
}
skip_codegen_passes:
if (bpf_jit_enable > 1)
/*
* Note that we output the base address of the code_base