* MIPS eBPF JIT support on pre-32R2 @ 2019-12-05 12:45 Alexander Lobakin 2019-12-05 13:04 ` Daniel Borkmann 2019-12-05 18:44 ` Paul Burton 0 siblings, 2 replies; 5+ messages in thread From: Alexander Lobakin @ 2019-12-05 12:45 UTC (permalink / raw) To: Paul Burton Cc: Hassan Naveed, Ralf Baechle, James Hogan, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko, netdev, bpf, linux-mips, linux-kernel 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: MIPS eBPF JIT support on pre-32R2 2019-12-05 12:45 MIPS eBPF JIT support on pre-32R2 Alexander Lobakin @ 2019-12-05 13:04 ` Daniel Borkmann 2019-12-05 18:44 ` Paul Burton 1 sibling, 0 replies; 5+ messages in thread From: Daniel Borkmann @ 2019-12-05 13:04 UTC (permalink / raw) To: Alexander Lobakin Cc: Paul Burton, Hassan Naveed, Ralf Baechle, James Hogan, Alexei Starovoitov, Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko, netdev, bpf, linux-mips, linux-kernel 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: MIPS eBPF JIT support on pre-32R2 2019-12-05 12:45 MIPS eBPF JIT support on pre-32R2 Alexander Lobakin 2019-12-05 13:04 ` Daniel Borkmann @ 2019-12-05 18:44 ` Paul Burton 2019-12-06 7:20 ` Alexander Lobakin 1 sibling, 1 reply; 5+ messages in thread From: Paul Burton @ 2019-12-05 18:44 UTC (permalink / raw) To: Alexander Lobakin Cc: Paul Burton, Hassan Naveed, Ralf Baechle, James Hogan, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko, netdev, bpf, linux-mips, linux-kernel 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/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 :) Thanks, Paul ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: MIPS eBPF JIT support on pre-32R2 2019-12-05 18:44 ` Paul Burton @ 2019-12-06 7:20 ` Alexander Lobakin 2019-12-06 8:11 ` Alexander Lobakin 0 siblings, 1 reply; 5+ messages in thread From: Alexander Lobakin @ 2019-12-06 7:20 UTC (permalink / raw) To: Paul Burton Cc: Paul Burton, Hassan Naveed, Ralf Baechle, James Hogan, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko, netdev, bpf, linux-mips, linux-kernel 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/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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: MIPS eBPF JIT support on pre-32R2 2019-12-06 7:20 ` Alexander Lobakin @ 2019-12-06 8:11 ` Alexander Lobakin 0 siblings, 0 replies; 5+ messages in thread From: Alexander Lobakin @ 2019-12-06 8:11 UTC (permalink / raw) To: Paul Burton Cc: Paul Burton, Hassan Naveed, Ralf Baechle, James Hogan, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko, netdev, bpf, linux-mips, linux-kernel 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-12-06 8:11 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-12-05 12:45 MIPS eBPF JIT support on pre-32R2 Alexander Lobakin 2019-12-05 13:04 ` Daniel Borkmann 2019-12-05 18:44 ` Paul Burton 2019-12-06 7:20 ` Alexander Lobakin 2019-12-06 8:11 ` Alexander Lobakin
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