On 2016/06/21 11:47AM, Thadeu Lima de Souza Cascardo wrote: > On Tue, Jun 21, 2016 at 09:15:48PM +1000, Michael Ellerman wrote: > > On Tue, 2016-06-21 at 14:28 +0530, Naveen N. Rao wrote: > > > On 2016/06/20 03:56PM, Thadeu Lima de Souza Cascardo wrote: > > > > On Sun, Jun 19, 2016 at 11:19:14PM +0530, Naveen N. Rao wrote: > > > > > On 2016/06/17 10:00AM, Thadeu Lima de Souza Cascardo wrote: > > > > > > > > > > > > Hi, Michael and Naveen. > > > > > > > > > > > > I noticed independently that there is a problem with BPF JIT and > > > > > > ABIv2, and > > > > > > worked out the patch below before I noticed Naveen's patchset and > > > > > > the latest > > > > > > changes in ppc tree for a better way to check for ABI versions. > > > > > > > > > > > > However, since the issue described below affect mainline and stable > > > > > > kernels, > > > > > > would you consider applying it before merging your two patchsets, > > > > > > so that we can > > > > > > more easily backport the fix? > > > > > > > > > > Hi Cascardo, > > > > > Given that this has been broken on ABIv2 since forever, I didn't > > > > > bother > > > > > fixing it. But, I can see why this would be a good thing to have for > > > > > -stable and existing distros. However, while your patch below may fix > > > > > the crash you're seeing on ppc64le, it is not sufficient -- you'll > > > > > need > > > > > changes in bpf_jit_asm.S as well. > > > > > > > > Hi, Naveen. > > > > > > > > Any tips on how to exercise possible issues there? Or what changes you > > > > think > > > > would be sufficient? > > > > > > The calling convention is different with ABIv2 and so we'll need changes > > > in bpf_slow_path_common() and sk_negative_common(). > > > > How big would those changes be? Do we know?
I don't think it'd be that much -- I will take a stab at this today. > > > > How come no one reported this was broken previously? This is the first I've > > heard of it being broken. > > > > I just heard of it less than two weeks ago, and only could investigate it last > week, when I realized mainline was also affected. > > It looks like the little-endian support for classic JIT were done before the > conversion to ABIv2. And as JIT is disabled by default, no one seems to have > exercised it. Yes, my thoughts too. I didn't previously think much about this as JIT wouldn't be enabled by default. It's interesting though that no one else reported this as an issue before. > > > > However, rather than enabling classic JIT for ppc64le, are we better off > > > just disabling it? > > > > > > --- a/arch/powerpc/Kconfig > > > +++ b/arch/powerpc/Kconfig > > > @@ -128,7 +128,7 @@ config PPC > > > select IRQ_FORCED_THREADING > > > select HAVE_RCU_TABLE_FREE if SMP > > > select HAVE_SYSCALL_TRACEPOINTS > > > - select HAVE_CBPF_JIT > > > + select HAVE_CBPF_JIT if CPU_BIG_ENDIAN > > > select HAVE_ARCH_JUMP_LABEL > > > select ARCH_HAVE_NMI_SAFE_CMPXCHG > > > select ARCH_HAS_GCOV_PROFILE_ALL > > > > > > > > > Michael, > > > Let me know your thoughts on whether you intend to take this patch or > > > Cascardo's patch for -stable before the eBPF patches. I can redo my > > > patches accordingly. > > > > This patch sounds like the best option at the moment for something we can > > backport. Unless the changes to fix it are minimal. Right -- I will take a look today to see what changes would be needed. - Naveen
