linux-kernel - Re: [PATCH 0/2] uprobes,mm: speculative lockless VMA-to-uprobe lookup

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Message-ID: <CAG48ez1+Y+ifc3HfG=E5j+g=RwtzH2TiE4mAC2TZxS52idkRZg@mail.gmail.com>
Date: Tue, 10 Sep 2024 18:06:12 +0200
From: Jann Horn <jannh@...gle.com>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, peterz@...radead.org, oleg@...hat.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, jolsa@...nel.org, paulmck@...nel.org, 
	willy@...radead.org, surenb@...gle.com, akpm@...ux-foundation.org, 
	linux-mm@...ck.org, mjguzik@...il.com, brauner@...nel.org
Subject: Re: [PATCH 0/2] uprobes,mm: speculative lockless VMA-to-uprobe lookup

On Fri, Sep 6, 2024 at 7:12 AM Andrii Nakryiko <andrii@...nel.org> wrote:
> Implement speculative (lockless) resolution of VMA to inode to uprobe,
> bypassing the need to take mmap_lock for reads, if possible. Patch #1 by Suren
> adds mm_struct helpers that help detect whether mm_struct were changed, which
> is used by uprobe logic to validate that speculative results can be trusted
> after all the lookup logic results in a valid uprobe instance.

Random thought: It would be nice if you could skip the MM stuff
entirely and instead go through the GUP-fast path, but I guess going
from a uprobe-created anon page to the corresponding uprobe is hard...
but maybe if you used the anon_vma pointer as a lookup key to find the
uprobe, it could work? Though then you'd need hooks in the anon_vma
code... maybe not such a great idea.