Hey all,
I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807:
if (!prog->jit_requested || MIPS_ISA_REV < 2)
return prog;
Do pre-32R2 architectures (32R1, maybe even R3000-like) actually support
this eBPF JIT code? If they do, then the condition 'MIPS_ISA_REV < 2'
should be removed as it is always true for them and tells CC to remove
JIT completely.
If they don't support instructions from this JIT, then the line
arch/mips/Kconfig:50:
select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
should be changed to something like:
select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
(and then the mentioned 'if' condition would become redundant)
At the moment it is possible to build a kernel without both JIT and
interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be allowed
I suppose?) within the following configuration:
- select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1);
- enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected);
- enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from
the system).
I may prepare a proper patch by myself if needed (after clarification).
Thanks.
Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
On Thu, Dec 05, 2019 at 03:45:27PM +0300, Alexander Lobakin wrote:
> Hey all,
>
> I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807:
>
> if (!prog->jit_requested || MIPS_ISA_REV < 2)
> return prog;
>
> Do pre-32R2 architectures (32R1, maybe even R3000-like) actually support
> this eBPF JIT code? If they do, then the condition 'MIPS_ISA_REV < 2'
> should be removed as it is always true for them and tells CC to remove
> JIT completely.
>
> If they don't support instructions from this JIT, then the line
> arch/mips/Kconfig:50:
>
> select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
>
> should be changed to something like:
>
> select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
>
> (and then the mentioned 'if' condition would become redundant)
>
> At the moment it is possible to build a kernel without both JIT and
> interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be allowed
> I suppose?) within the following configuration:
Cannot comment on the MIPS ISA question above, but it would definiely be
a bug to build a kernel with neither JIT nor interpreter. If a JIT is not
available, then there /must/ be the interpreter as fallback to be able to
run BPF programs.
> - select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1);
> - enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected);
> - enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from
> the system).
>
> I may prepare a proper patch by myself if needed (after clarification).
> Thanks.
>
> Regards,
> ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
Hi Alexander,
On Thu, Dec 05, 2019 at 03:45:27PM +0300, Alexander Lobakin wrote:
> Hey all,
>
> I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807:
>
> if (!prog->jit_requested || MIPS_ISA_REV < 2)
> return prog;
>
> Do pre-32R2 architectures (32R1, maybe even R3000-like) actually support
> this eBPF JIT code?
No, they don't; the eBPF JIT makes unconditional use of at least the
(d)ins & (d)ext instructions which were added in MIPSr2, so it would
result in reserved instruction exceptions & panics if enabled on
pre-MIPSr2 CPUs.
> If they do, then the condition 'MIPS_ISA_REV < 2'
> should be removed as it is always true for them and tells CC to remove
> JIT completely.
>
> If they don't support instructions from this JIT, then the line
> arch/mips/Kconfig:50:
>
> select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
>
> should be changed to something like:
>
> select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
>
> (and then the mentioned 'if' condition would become redundant)
Good spot; I agree entirely, this dependency should be reflected in
Kconfig.
> At the moment it is possible to build a kernel without both JIT and
> interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be allowed
> I suppose?) within the following configuration:
>
> - select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1);
> - enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected);
> - enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from
> the system).
>
> I may prepare a proper patch by myself if needed (after clarification).
That would be great, thanks!
One thing to note is that I hope we'll restore the cBPF JIT with this
patch:
https://lore.kernel.org/linux-mips/[email protected]/T/#u
The cBPF JIT looks like it should work on older pre-MIPSr2 CPUs, so the
only way this is relevant is that your patch might have a minor
conflict. But I thought I'd mention it anyway :)
Thanks,
Paul
Paul Burton wrote 05.12.2019 21:44:
> Hi Alexander,
Hi Paul!
> On Thu, Dec 05, 2019 at 03:45:27PM +0300, Alexander Lobakin wrote:
>> Hey all,
>>
>> I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807:
>>
>> if (!prog->jit_requested || MIPS_ISA_REV < 2)
>> return prog;
>>
>> Do pre-32R2 architectures (32R1, maybe even R3000-like) actually
>> support
>> this eBPF JIT code?
>
> No, they don't; the eBPF JIT makes unconditional use of at least the
> (d)ins & (d)ext instructions which were added in MIPSr2, so it would
> result in reserved instruction exceptions & panics if enabled on
> pre-MIPSr2 CPUs.
>
>> If they do, then the condition 'MIPS_ISA_REV < 2'
>> should be removed as it is always true for them and tells CC to remove
>> JIT completely.
>>
>> If they don't support instructions from this JIT, then the line
>> arch/mips/Kconfig:50:
>>
>> select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
>>
>> should be changed to something like:
>>
>> select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
>>
>> (and then the mentioned 'if' condition would become redundant)
>
> Good spot; I agree entirely, this dependency should be reflected in
> Kconfig.
>
>> At the moment it is possible to build a kernel without both JIT and
>> interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be allowed
>> I suppose?) within the following configuration:
>>
>> - select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1);
>> - enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected);
>> - enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from
>> the system).
>>
>> I may prepare a proper patch by myself if needed (after
>> clarification).
>
> That would be great, thanks!
Great, I'll send it in about ~2-3 hours.
> One thing to note is that I hope we'll restore the cBPF JIT with this
> patch:
>
> https://lore.kernel.org/linux-mips/[email protected]/T/#u
>
> The cBPF JIT looks like it should work on older pre-MIPSr2 CPUs, so the
> only way this is relevant is that your patch might have a minor
> conflict. But I thought I'd mention it anyway :)
Yes, I thought about this too. If pre-32R2 CPUs don't support our eBPF
JIT, we'd better restore cBPF for them, so they could speed-up at least
"classic" instructions. Glad you've decided to do that.
> Thanks,
> Paul
Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
Alexander Lobakin писал 06.12.2019 10:20:
> Paul Burton wrote 05.12.2019 21:44:
>> Hi Alexander,
>
> Hi Paul!
>
>> On Thu, Dec 05, 2019 at 03:45:27PM +0300, Alexander Lobakin wrote:
>>> Hey all,
>>>
>>> I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807:
>>>
>>> if (!prog->jit_requested || MIPS_ISA_REV < 2)
>>> return prog;
>>>
>>> Do pre-32R2 architectures (32R1, maybe even R3000-like) actually
>>> support
>>> this eBPF JIT code?
>>
>> No, they don't; the eBPF JIT makes unconditional use of at least the
>> (d)ins & (d)ext instructions which were added in MIPSr2, so it would
>> result in reserved instruction exceptions & panics if enabled on
>> pre-MIPSr2 CPUs.
>>
>>> If they do, then the condition 'MIPS_ISA_REV < 2'
>>> should be removed as it is always true for them and tells CC to
>>> remove
>>> JIT completely.
>>>
>>> If they don't support instructions from this JIT, then the line
>>> arch/mips/Kconfig:50:
>>>
>>> select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
>>>
>>> should be changed to something like:
>>>
>>> select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
>>>
>>> (and then the mentioned 'if' condition would become redundant)
>>
>> Good spot; I agree entirely, this dependency should be reflected in
>> Kconfig.
>>
>>> At the moment it is possible to build a kernel without both JIT and
>>> interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be
>>> allowed
>>> I suppose?) within the following configuration:
>>>
>>> - select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1);
>>> - enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected);
>>> - enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from
>>> the system).
>>>
>>> I may prepare a proper patch by myself if needed (after
>>> clarification).
>>
>> That would be great, thanks!
>
> Great, I'll send it in about ~2-3 hours.
Here we are: [1]
Yep, this will conflict with your patch restoring cBPF for MIPS32.
If you have any questions about my patch or I should change anything in
it, please let me know.
Thanks!
>> One thing to note is that I hope we'll restore the cBPF JIT with this
>> patch:
>>
>> https://lore.kernel.org/linux-mips/[email protected]/T/#u
>>
>> The cBPF JIT looks like it should work on older pre-MIPSr2 CPUs, so
>> the
>> only way this is relevant is that your patch might have a minor
>> conflict. But I thought I'd mention it anyway :)
>
> Yes, I thought about this too. If pre-32R2 CPUs don't support our eBPF
> JIT, we'd better restore cBPF for them, so they could speed-up at least
> "classic" instructions. Glad you've decided to do that.
>
>> Thanks,
>> Paul
>
> Regards,
> ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
[1]
https://lore.kernel.org/linux-mips/[email protected]/
Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ