netdev - bpf: bpf_probe_read helper restriction on s390x

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Date:   Sun, 5 Jul 2020 21:42:25 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     linux-s390@...r.kernel.org,
        Sumanth Korikkar <Sumanth.Korikkar@....com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Yauheni Kaliuta <yauheni.kaliuta@...hat.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Brendan Gregg <brendan.d.gregg@...il.com>, bas@...lab.org,
        Matheus Marchini <mat@...rchini.me>, Daniel Xu <dxu@...uu.xyz>
Subject: bpf: bpf_probe_read helper restriction on s390x

hi,
with following commit:
  0ebeea8ca8a4 bpf: Restrict bpf_probe_read{, str}() only to archs where they work

the bpf_probe_read BPF helper is restricted on architectures that
have 'non overlapping address space' and select following config:

   select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

there's also nice explanation in this commit's changelog:
  6ae08ae3dea2 bpf: Add probe_read_{user, kernel} and probe_read_{user, kernel}_str helpers


We have a problem with bpftrace not working properly on s390x because
bpf_probe_read is no longer available, and bpftrace does not use
bpf_probe_read_(user/kernel) variants yet.

My question is if s390x is 'arch with overlapping address space' and we
could fix this by adding ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE for s390x
or we need to fix bpftrace to detect this, which we probably need to do
in any case ;-)

thanks,
jirka