Re: [PATCH] ppc: Fix BPF JIT for ABIv2

On 2016/06/22 12:42PM, Naveen N Rao wrote:

On 2016/06/21 11:47AM, Thadeu Lima de Souza Cascardo wrote:

quoted

On Tue, Jun 21, 2016 at 09:15:48PM +1000, Michael Ellerman wrote:

quoted

On Tue, 2016-06-21 at 14:28 +0530, Naveen N. Rao wrote:

quoted

On 2016/06/20 03:56PM, Thadeu Lima de Souza Cascardo wrote:

quoted

On Sun, Jun 19, 2016 at 11:19:14PM +0530, Naveen N. Rao wrote:

quoted

On 2016/06/17 10:00AM, Thadeu Lima de Souza Cascardo wrote:

quoted

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?

So, this does need quite a few changes:
- the skb helpers need to emit code to setup TOC and the JIT code needs 
  to be updated to setup r12.
- the slow path code needs to be changed to store r3 elsewhere on ABIv2
- the above also means we need to change the stack macros with the 
  proper ABIv2 values
- the little endian support isn't complete as well -- some of the skb 
  helpers are not using byte swap instructions.

As such, I think we should just disable classic JIT on ppc64le.


- Naveen