linux-kernel - Re: [PATCH v5 18/22] docs: add documentation for memfd preservation via LUO

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <mafs01pm1amwo.fsf@kernel.org>
Date: Thu, 13 Nov 2025 17:59:51 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: pratyush@...nel.org,  jasonmiu@...gle.com,  graf@...zon.com,
  rppt@...nel.org,  dmatlack@...gle.com,  rientjes@...gle.com,
  corbet@....net,  rdunlap@...radead.org,  ilpo.jarvinen@...ux.intel.com,
  kanie@...ux.alibaba.com,  ojeda@...nel.org,  aliceryhl@...gle.com,
  masahiroy@...nel.org,  akpm@...ux-foundation.org,  tj@...nel.org,
  yoann.congal@...le.fr,  mmaurer@...gle.com,  roman.gushchin@...ux.dev,
  chenridong@...wei.com,  axboe@...nel.dk,  mark.rutland@....com,
  jannh@...gle.com,  vincent.guittot@...aro.org,  hannes@...xchg.org,
  dan.j.williams@...el.com,  david@...hat.com,  joel.granados@...nel.org,
  rostedt@...dmis.org,  anna.schumaker@...cle.com,  song@...nel.org,
  zhangguopeng@...inos.cn,  linux@...ssschuh.net,
  linux-kernel@...r.kernel.org,  linux-doc@...r.kernel.org,
  linux-mm@...ck.org,  gregkh@...uxfoundation.org,  tglx@...utronix.de,
  mingo@...hat.com,  bp@...en8.de,  dave.hansen@...ux.intel.com,
  x86@...nel.org,  hpa@...or.com,  rafael@...nel.org,  dakr@...nel.org,
  bartosz.golaszewski@...aro.org,  cw00.choi@...sung.com,
  myungjoo.ham@...sung.com,  yesanishhere@...il.com,
  Jonathan.Cameron@...wei.com,  quic_zijuhu@...cinc.com,
  aleksander.lobakin@...el.com,  ira.weiny@...el.com,
  andriy.shevchenko@...ux.intel.com,  leon@...nel.org,  lukas@...ner.de,
  bhelgaas@...gle.com,  wagi@...nel.org,  djeffery@...hat.com,
  stuart.w.hayes@...il.com,  lennart@...ttering.net,  brauner@...nel.org,
  linux-api@...r.kernel.org,  linux-fsdevel@...r.kernel.org,
  saeedm@...dia.com,  ajayachandra@...dia.com,  jgg@...dia.com,
  parav@...dia.com,  leonro@...dia.com,  witu@...dia.com,
  hughd@...gle.com,  skhawaja@...gle.com,  chrisl@...nel.org
Subject: Re: [PATCH v5 18/22] docs: add documentation for memfd preservation
 via LUO

On Thu, Nov 13 2025, Pasha Tatashin wrote:

>> +Limitations
>> +===========
>> +
>> +The current implementation has the following limitations:
>> +
>> +Size
>> +  Currently the size of the file is limited by the size of the FDT. The FDT can
>> +  be at of most ``MAX_PAGE_ORDER`` order. By default this is 4 MiB with 4K
>> +  pages. Each page in the file is tracked using 16 bytes. This limits the
>> +  maximum size of the file to 1 GiB.
>
> The above should be removed, as we are using KHO vmalloc that resolves
> this limitation. Pratyush, I suggest for v6 let's move memfd
> documnetation right into the code: memfd_luo.c and
> liveupdate/abi/memfd.h, and source it from there.

ACK. I think the section on behavior in different phases is also out of
date now, and the serialization format too. The format is more
accurately defined in include/linux/liveupdate/abi/memfd.h. So this
documentation needs an overhaul.

I don't mind moving it to the code and including it in the HTML docs via
kernel-doc. Will do that for the next revision.

>
> Keeping documentation with the code helps reduce code/doc divergence.
>
> Pasha

-- 
Regards,
Pratyush Yadav