linux-kernel - Re: [RFC PATCH v2 0/1] Introduce vmap

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] [day] [month] [year] [list]

Message-ID: <Z-wi-f9WTQ8PiWtW@fedora>
Date: Tue, 1 Apr 2025 10:31:37 -0700
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Huan Yang <link@...o.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Brendan Jackman <jackmanb@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 0/1] Introduce vmap_file()

On Tue, Apr 01, 2025 at 02:08:53PM +0800, Huan Yang wrote:
> 
> 在 2025/4/1 11:19, Vishal Moola (Oracle) 写道:
> > On Tue, Apr 01, 2025 at 10:21:46AM +0800, Huan Yang wrote:
> > > 在 2025/4/1 09:50, Vishal Moola (Oracle) 写道:
> > > > On Mon, Mar 31, 2025 at 10:05:53AM +0800, Huan Yang wrote:
> > > > > HI Vishal,
> > > > > 
> > > > > 在 2025/3/29 05:13, Vishal Moola (Oracle) 写道:
> > > > > > Currently, users have to call vmap() or vmap_pfn() to map pages to
> > > > > > kernel virtual space. vmap_pfn() is for special pages (i.e. pfns
> > > > > > without struct page). vmap() handles normal pages.
> > > > > > 
> > > > > > With large folios, we may want to map ranges that only span
> > > > > > part of a folio (i.e. mapping half of a 2Mb folio).
> > > > > > vmap_file() will allow us to do so.
> > > > > You mention vmap_file can support range folio vmap, but when I look code, I can't figure out
> > > > > 
> > > > > how to use, maybe I missed something? :)
> > > > I took a look at the udma-buf code. Rather than iterating through the
> > > > folios using pfns, you can calculate the corresponding file offsets
> > > > (maybe you already have them?) to map the desired folios.
> > > Currently udmabuf folio's not simple based on file(even each memory from memfd). User can provide
> > > 
> > > random range of memfd  to udmabuf to use. For example:
> > > 
> > > We get a memfd maybe 4M, user split it into [0, 2M), [1M, 2M), [2M, 4M), so you can see 1M-2M range repeat.
> > > 
> > > This range can gathered by udmabuf_create_list, then udmabuf use it. So, udmabuf record it by folio array+offset array.
> > I was thinking you could call vmap_file() on every sub-range and use
> > those addresses. It should work, we'd have to look at making udmabuf api's
> > support it.
> 
> Hmmm, how to get contigous virtual address? Or there are a way to merge each split vmap's return address?

I'm not sure, I'd have to take a look at that. Maybe going into a large
folio world that might be a useful expansion on the APIs?

> IMO, user invoke vmap want to map each scatter memory into contigous virtual address, but as your suggestion,
> 
> I think can't to this. :)

We could discuss vmap_file() supporting a series of offsets to map
portions of a file; I think thats a reasonable ask for the general API.

We could potentially do multiple files as well, but things start getting
really complex at that point so I'd like to avoid that.

The Udma code looks to be doing some buggy stuff, so I'd prefer
we look at fixing/reworking those before hacking in a 'generic' API just
so they can keep doing that.