diff mbox series

[bpf-next,v3,1/2] bpf, x64: Propagate tailcall info only for subprogs

Message ID 20241107134529.8602-2-leon.hwang@linux.dev (mailing list archive)
State Accepted
Commit a1087da9d11e5bcacc706002bc0f84b790881f69
Delegated to: BPF
Headers show
Series bpf, x64: Introduce two tailcall enhancements | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 5 this patch: 5
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 14 maintainers not CCed: mingo@redhat.com dave.hansen@linux.intel.com x86@kernel.org kpsingh@kernel.org hpa@zytor.com martin.lau@linux.dev tglx@linutronix.de bp@alien8.de dsahern@kernel.org netdev@vger.kernel.org sdf@fomichev.me song@kernel.org john.fastabend@gmail.com haoluo@google.com
netdev/build_clang success Errors and warnings before: 3 this patch: 3
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
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netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 12 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
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Commit Message

Leon Hwang Nov. 7, 2024, 1:45 p.m. UTC 
In x64 JIT, propagate tailcall info only for subprogs, not for helpers
or kfuncs.

Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 arch/x86/net/bpf_jit_comp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Alexei Starovoitov Nov. 13, 2024, 1:31 a.m. UTC | #1 
On Thu, Nov 7, 2024 at 5:46 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> In x64 JIT, propagate tailcall info only for subprogs, not for helpers
> or kfuncs.
>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---
>  arch/x86/net/bpf_jit_comp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 06b080b61aa57..eb08cc6d66401 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2124,10 +2124,11 @@ st:                     if (is_imm8(insn->off))
>
>                         /* call */
>                 case BPF_JMP | BPF_CALL: {
> +                       bool pseudo_call = src_reg == BPF_PSEUDO_CALL;
>                         u8 *ip = image + addrs[i - 1];
>
>                         func = (u8 *) __bpf_call_base + imm32;
> -                       if (tail_call_reachable) {
> +                       if (pseudo_call && tail_call_reachable) {
>                                 LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
>                                 ip += 7;
>                         }

I've applied this patch with this tweak:
if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable)

I don't see much value in patch 2.
The tail_call feature is an old approach. It is now causing
maintenance issues with other features.
I'd rather not touch anything tail call related.
So I dropped patch 2.

I'd like to see proper indirect goto and indirect call
support being developed further.
Anton started working on it, but dropped the ball.
We need to commandeer the patches.
Leon Hwang Nov. 13, 2024, 1:53 a.m. UTC | #2 
On 13/11/24 09:31, Alexei Starovoitov wrote:
> On Thu, Nov 7, 2024 at 5:46 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> In x64 JIT, propagate tailcall info only for subprogs, not for helpers
>> or kfuncs.
>>
>> Acked-by: Yonghong Song <yonghong.song@linux.dev>
>> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
>> ---
>>  arch/x86/net/bpf_jit_comp.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>> index 06b080b61aa57..eb08cc6d66401 100644
>> --- a/arch/x86/net/bpf_jit_comp.c
>> +++ b/arch/x86/net/bpf_jit_comp.c
>> @@ -2124,10 +2124,11 @@ st:                     if (is_imm8(insn->off))
>>
>>                         /* call */
>>                 case BPF_JMP | BPF_CALL: {
>> +                       bool pseudo_call = src_reg == BPF_PSEUDO_CALL;
>>                         u8 *ip = image + addrs[i - 1];
>>
>>                         func = (u8 *) __bpf_call_base + imm32;
>> -                       if (tail_call_reachable) {
>> +                       if (pseudo_call && tail_call_reachable) {
>>                                 LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
>>                                 ip += 7;
>>                         }
> 
> I've applied this patch with this tweak:
> if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable)
> 
> I don't see much value in patch 2.
> The tail_call feature is an old approach. It is now causing
> maintenance issues with other features.
> I'd rather not touch anything tail call related.
> So I dropped patch 2.
> 
> I'd like to see proper indirect goto and indirect call
> support being developed further.
> Anton started working on it, but dropped the ball.
> We need to commandeer the patches.

Great to see jmp table supporting tail call.

Thanks,
Leon
Anton Protopopov Nov. 13, 2024, 2:14 a.m. UTC | #3 
On 24/11/12 05:31PM, Alexei Starovoitov wrote:
> On Thu, Nov 7, 2024 at 5:46 AM Leon Hwang <leon.hwang@linux.dev> wrote:
> >
> > In x64 JIT, propagate tailcall info only for subprogs, not for helpers
> > or kfuncs.
> >
> > Acked-by: Yonghong Song <yonghong.song@linux.dev>
> > Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> > ---
> >  arch/x86/net/bpf_jit_comp.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 06b080b61aa57..eb08cc6d66401 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -2124,10 +2124,11 @@ st:                     if (is_imm8(insn->off))
> >
> >                         /* call */
> >                 case BPF_JMP | BPF_CALL: {
> > +                       bool pseudo_call = src_reg == BPF_PSEUDO_CALL;
> >                         u8 *ip = image + addrs[i - 1];
> >
> >                         func = (u8 *) __bpf_call_base + imm32;
> > -                       if (tail_call_reachable) {
> > +                       if (pseudo_call && tail_call_reachable) {
> >                                 LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
> >                                 ip += 7;
> >                         }
> 
> I've applied this patch with this tweak:
> if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable)
> 
> I don't see much value in patch 2.
> The tail_call feature is an old approach. It is now causing
> maintenance issues with other features.
> I'd rather not touch anything tail call related.
> So I dropped patch 2.
> 
> I'd like to see proper indirect goto and indirect call
> support being developed further.
> Anton started working on it, but dropped the ball.
> We need to commandeer the patches.

Actually, I am still on it. I will start sending patches this week.
Alexei Starovoitov Nov. 13, 2024, 2:15 a.m. UTC | #4 
On Tue, Nov 12, 2024 at 6:11 PM Anton Protopopov <aspsk@isovalent.com> wrote:
>
> Actually, I am still on it. I will start sending patches this week.

Ohh. Great. Cannot wait.
diff mbox series

Patch

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 06b080b61aa57..eb08cc6d66401 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2124,10 +2124,11 @@  st:			if (is_imm8(insn->off))
 
 			/* call */
 		case BPF_JMP | BPF_CALL: {
+			bool pseudo_call = src_reg == BPF_PSEUDO_CALL;
 			u8 *ip = image + addrs[i - 1];
 
 			func = (u8 *) __bpf_call_base + imm32;
-			if (tail_call_reachable) {
+			if (pseudo_call && tail_call_reachable) {
 				LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
 				ip += 7;
 			}