linux-kernel - Re: [PATCH] ppc: Fix BPF JIT for ABIv2

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Date:	Tue, 21 Jun 2016 14:28:07 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, Matt Evans <matt@...abs.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...com>,
	Denis Kirjanov <kda@...ux-powerpc.org>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [PATCH] ppc: Fix BPF JIT for ABIv2

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().

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.


- Naveen