[PATCH] powerpc/bpf: populate extable entries only during the last pass

[Hari Bathini]

Hello Christophe,

Thanks for the review.

On 07/04/23 11:31 am, Christophe Leroy wrote:
> 
> 
> Le 06/04/2023 à 09:35, Hari Bathini a écrit :
>> Since commit 85e031154c7c ("powerpc/bpf: Perform complete extra passes
>> to update addresses"), two additional passes are performed to avoid
>> space and CPU time wastage on powerpc. But these extra passes led to
>> WARN_ON_ONCE() hits in bpf_add_extable_entry(). Fix it by not adding
>> extable entries during the extra pass.
> 
> Are you sure this change is correct ?

Actually, I was in two minds about that owing to commit 04c04205bc35
("bpf powerpc: Remove extra_pass from bpf_jit_build_body()").

> During the extra pass the code can get shrinked or expanded (within the
> limits of the size of the preliminary pass). Shouldn't extable entries
> be populated during the last pass ?

Unlikely, but the intention there was to eliminate a regression in case
extra_pass ends up being 'false' always in any subsequent change.

- Hari

>>
>> Fixes: 85e031154c7c ("powerpc/bpf: Perform complete extra passes to update addresses")
>> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
>> ---
>>    arch/powerpc/net/bpf_jit_comp32.c | 2 +-
>>    arch/powerpc/net/bpf_jit_comp64.c | 2 +-
>>    2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
>> index 7f91ea064c08..e788b1fbeee6 100644
>> --- a/arch/powerpc/net/bpf_jit_comp32.c
>> +++ b/arch/powerpc/net/bpf_jit_comp32.c
>> @@ -977,7 +977,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>>    			if (size != BPF_DW && !fp->aux->verifier_zext)
>>    				EMIT(PPC_RAW_LI(dst_reg_h, 0));
>>    
>> -			if (BPF_MODE(code) == BPF_PROBE_MEM) {
>> +			if (BPF_MODE(code) == BPF_PROBE_MEM && !extra_pass) {
>>    				int insn_idx = ctx->idx - 1;
>>    				int jmp_off = 4;
>>    
>> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
>> index 8dd3cabaa83a..1cc2777ec846 100644
>> --- a/arch/powerpc/net/bpf_jit_comp64.c
>> +++ b/arch/powerpc/net/bpf_jit_comp64.c
>> @@ -921,7 +921,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>>    			if (size != BPF_DW && insn_is_zext(&insn[i + 1]))
>>    				addrs[++i] = ctx->idx * 4;
>>    
>> -			if (BPF_MODE(code) == BPF_PROBE_MEM) {
>> +			if (BPF_MODE(code) == BPF_PROBE_MEM && !extra_pass) {
>>    				ret = bpf_add_extable_entry(fp, image, pass, ctx, ctx->idx - 1,
>>    							    4, dst_reg);
>>    				if (ret)