linux-kernel - Re: [PATCH v3 29/30] luo: allow preserving memfd

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: <aLiZbb_F5R2x9-y2@kernel.org>
Date: Wed, 3 Sep 2025 22:39:25 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Jason Gunthorpe <jgg@...dia.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>, jasonmiu@...gle.com,
	graf@...zon.com, changyuanl@...gle.com, 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, parav@...dia.com, leonro@...dia.com,
	witu@...dia.com
Subject: Re: [PATCH v3 29/30] luo: allow preserving memfd

Hi Pratyush,

On Wed, Sep 03, 2025 at 04:17:15PM +0200, Pratyush Yadav wrote:
> On Tue, Sep 02 2025, Mike Rapoport wrote:
> >
> > As for porting kho_preserve_vmalloc() to kho_array, I also feel that it
> > would just make kho_preserve_vmalloc() more complex and I'd rather simplify
> > it even more, e.g. with preallocating all the pages that preserve indices
> > in advance.
> 
> I think there are two parts here. One is the data format of the KHO
> array and the other is the way to build it. I think the format is quite
> simple and versatile, and we can have many strategies of building it.
> 
> For example, if you are only concerned with pre-allocating data, I can
> very well add a way to initialize the KHO array with with a fixed size
> up front.

I wasn't concerned with preallocation vs allocating a page at a time, I
though with preallocation the vmalloc code will become even simpler, but
it's not :)
 
> Beyond that, I think KHO array will actually make kho_preserve_vmalloc()
> simpler since it won't have to deal with the linked list traversal
> logic. It can just do ka_for_each() and just get all the pages.
>
> We can also convert the preservation bitmaps to use it so the linked list
> logic is in one place, and others just build on top of it.

I disagree. The boilerplate to initialize and iterate the kho_array will
not make neither vmalloc nor bitmaps preservation simpler IMO.

And for bitmaps Pasha and Jason M. are anyway working on a different data
structure already, so if their proposal moves forward converting bitmap
preservation to anything would be a wasted effort.

> -- 
> Regards,
> Pratyush Yadav

-- 
Sincerely yours,
Mike.