Messages in this thread | | | Date | Fri, 06 Dec 2019 11:11:40 +0300 | From | Alexander Lobakin <> | Subject | Re: MIPS eBPF JIT support on pre-32R2 |
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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/20191205182318.2761605-1-paulburton@kernel.org/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/20191206080741.12306-1-alobakin@dlink.ru/
Regards, ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
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