Re: [REGRESSION] bpf verifier slowdown due to vrealloc() change since 6.15-rc6

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

On Thu, May 15, 2025 at 10:52:13AM -0700, Pawan Gupta wrote:
> On Thu, May 15, 2025 at 10:41:41AM -0700, Kees Cook wrote:
> > On Thu, May 15, 2025 at 10:18:21AM -0700, Pawan Gupta wrote:
> > > On Thu, May 15, 2025 at 09:51:15AM -0700, Kees Cook wrote:
> > > > On Thu, May 15, 2025 at 07:51:26AM -0700, Kees Cook wrote:
> > > > > On May 15, 2025 6:12:25 AM PDT, Shung-Hsi Yu <shung-hsi.yu@suse.com> wrote:
> > > > > >There is an observable slowdown when running BPF selftests on 6.15-rc6
> > > > > >kernel[1] built with tools/testing/selftests/bpf/{config,config.x86_64}.
> > > > > [...]
> > > > > Where can I find the .config for the slow runs?
> > > > 
> > > > Oops, I can read. :) Doing a build now...
> > > > 
> > > > > And how do I run the test myself directly?
> > > > 
> > > > I found:
> > > > https://docs.kernel.org/bpf/bpf_devel_QA.html
> > > > 
> > > > But it doesn't seem to cover a bunch of stuff (no way to prebuild the
> > > > tests, no info on building the test modules).
> > > > 
> > > > This seems to be needed:
> > > > 
> > > > make O=regression-bug -C tools/testing/selftests/bpf/test_kmods
> > > > 
> > > > But then the booted kernel doesn't load it (missing signatures?)
> > > > 
> > > > Anyway, I'll keep digging...
> > > 
> > > After struggling with this for a while, I figured vmtest.sh is the easiest
> > > way to test bpf:
> > > 
> > > ./tools/testing/selftests/bpf/vmtest.sh -i ./test_progs
> > 
> > I can't even build the test_progs. :(
> > 
> > $ make test_progs
> > ...
> >   CLNG-BPF [test_progs] bpf_iter_tasks.bpf.o
> > progs/bpf_iter_tasks.c:98:8: error: call to undeclared function 'bpf_copy_from_user_task_str'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >    98 |         ret = bpf_copy_from_user_task_str((char *)task_str1, sizeof(task_str1), ptr, task, 0
> > );
> >       |               ^
> > 1 error generated.
> 
> I just tried on the latest upstream, and I am getting the same error. My
> earlier bisection was on a stable-rc for 6.14.y:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?h=linux-6.14.y
> 
> ... where it was first reported:
> 
> https://lore.kernel.org/stable/20250515041659.smhllyarxdwp7cav@desk/

I can confirm on v6.14.7-rc2 the test verif_scale_loop3_fail is now
passing(in <10 secs) after applying your first patch (mm: vmalloc: Actually
use the in-place vrealloc region). The the test passes after applying your
second patch also.

For some reason I am unable to build the bpf selftests on latest upstream.
I may be missing something that is required on latest upstream :-(