linux-kernel - Re: [PATCH] alloc_tag: introduce Kconfig option for default compressed profiling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJuCfpE3JgJVB3+-ZZPU3kFDjPSJyo4WFtwmtMUnXJ6q0E09dA@mail.gmail.com>
Date: Thu, 17 Apr 2025 09:00:59 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Usama Arif <usamaarif642@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	linux-mm@...ck.org, hannes@...xchg.org, linux-kernel@...r.kernel.org, 
	kernel-team@...a.com
Subject: Re: [PATCH] alloc_tag: introduce Kconfig option for default
 compressed profiling

On Thu, Apr 17, 2025 at 8:47 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> On Wed, Apr 16, 2025 at 05:11:11PM -0700, Suren Baghdasaryan wrote:
> > On Wed, Apr 16, 2025 at 2:41 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> > >
> > > On Wed, Apr 16, 2025 at 02:08:31PM -0700, Suren Baghdasaryan wrote:
> > > > On Wed, Apr 16, 2025 at 11:06 AM Usama Arif <usamaarif642@...il.com> wrote:
> > > > >
> > > > > With this Kconfig option enabled, the kernel stores allocation tag references
> > > > > in the page flags by default.
> > > > >
> > > > > There are 2 reasons to introduce this:
> > > > > - As mentioned in [1], compressed tags dont have system memory overhead
> > > > > and much lower performance overhead. It would be preferrable to have this as
> > > > > the default option, and to be able to switch it at compile time. Another
> > > > > option is to just declare the static key as true by default?
> > > > > - As compressed option is the best one, it doesn't make sense to have to
> > > > > change both defconfig and command line options to enable memory
> > > > > allocation profiling. Changing commandline across a large number of services
> > > > > can result in signifcant work, which shouldn't be needed if the kernel
> > > > > defconfig needs to be changed anyways.
> > > >
> > > > The reason tag compression is not the default option is because it
> > > > works only if there are enough free bits in the page flags to store a
> > > > tag index. If you configure it to use page flags and your build does
> > > > not have enough free bits, the profiling will be disabled (see
> > > > alloc_tag_sec_init()).
> > >
> > > Is it possible to fail the build in that case i.e. check the page flags
> > > availability at build time?
> >
> > The difficulty is finding out the number of allocation tags in the
> > kernel before it gets built. Maybe there is a way to add an additional
> > post-build stage to run that check.
>
> Yeah that would be good to have.
>
> > But even then making this option
> > default and causing build failures does not seem like a good idea to
> > me but maybe I'm being too cautious?
>
> Oh my question was orthogonal to the patch. Basically some users may
> want build time guarantee for this and they can enable such
> build-failing opt-in config/check.

Yes, that would require the post-build step to check the number of
tags vs the number of available page flag bits. I'll add it to my TODO
list but it won't be at the top, sorry :) Volunteers to help with that
would be highly appreciated.