linux-kernel - Re: [PATCH 2/3] mm: provide mapping_wrprotect

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: <Z6Gnat93skcoFZqn@infradead.org>
Date: Mon, 3 Feb 2025 21:36:42 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jaya Kumar <jayakumar.lkml@...il.com>,
	Simona Vetter <simona@...ll.ch>, Helge Deller <deller@....de>,
	linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Matthew Wilcox <willy@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	Kajtar Zsolt <soci@....rulez.org>, Maira Canal <mcanal@...lia.com>,
	Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH 2/3] mm: provide mapping_wrprotect_page() function

Hi Simona,


On Mon, Feb 03, 2025 at 04:49:34PM +0100, Simona Vetter wrote:
> 
> Could we go one step further and entirely drop the struct page? Similar to
> unmap_mapping_range for VM_SPECIAL mappings, except it only updates the
> write protection. The reason is that ideally we'd like fbdev defio to
> entirely get rid of any struct page usage, because with some dma_alloc()
> memory regions there's simply no struct page for them (it's a carveout).

Umm, for dma_alloc* where * is not _pages you never can get a page or
PFN form them.  They are block boxes and drivers must not attempt to
translated them into either a page or PFN or things will go wrong.
Only the kernel virtual address and dma_address may be used.

> See e.g.  Sa498d4d06d6 ("drm/fbdev-dma: Only install deferred I/O if
> necessary") for some of the pain this has caused.

The commit hash is corrupted, I guess this is 5a498d4d06d6 as the
subject line matches.  And that commit (just like the code it is trying
to fix) is completely broken as it violates the above.