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Date:   Wed, 8 Sep 2021 11:15:27 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Luigi Rizzo <lrizzo@google.com>, Yonghong Song <yhs@fb.com>,
        Liam Howlett <liam.howlett@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Michel Lespinasse <walken@google.com>,
        bpf <bpf@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        "kernel-team@fb.com" <kernel-team@fb.com>
Subject: Re: [PATCH mm/bpf v2] mm: bpf: add find_vma_no_check() without
 lockdep_assert on mm->mmap_lock
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On Wed, 8 Sep 2021 11:02:58 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> > Please describe the expected userspace-visible change from Peter's
> > patch in full detail?
> 
> User space expects build_id to be available. Peter patch simply removes
> that feature.

Are you sure?  He ends up with

static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
					  u64 *ips, u32 trace_nr, bool user)
{
	int i;

	/* cannot access current->mm, fall back to ips */
	for (i = 0; i < trace_nr; i++) {
		id_offs[i].status = BPF_STACK_BUILD_ID_IP;
		id_offs[i].ip = ips[i];
		memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
	}
	return;
}

and you're saying that userspace won't like this because we didn't set
BPF_STACK_BUILD_ID_VALID?