linux-kernel - Re: [PATCH v4 03/13] drm/shmem-helper: Map huge pages in fault handlers

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: <aO_ZmA6yoqbzTKt9@casper.infradead.org>
Date: Wed, 15 Oct 2025 18:27:52 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Loïc Molinari <loic.molinari@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Boris Brezillon <boris.brezillon@...labora.com>,
	Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
	Liviu Dudau <liviu.dudau@....com>, Melissa Wen <mwen@...lia.com>,
	Maíra Canal <mcanal@...lia.com>,
	Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Mikołaj Wasiak <mikolaj.wasiak@...el.com>,
	Christian Brauner <brauner@...nel.org>,
	Nitin Gote <nitin.r.gote@...el.com>,
	Andi Shyti <andi.shyti@...ux.intel.com>,
	Jonathan Corbet <corbet@....net>,
	Christopher Healy <healych@...zon.com>,
	Bagas Sanjaya <bagasdotme@...il.com>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v4 03/13] drm/shmem-helper: Map huge pages in fault
 handlers

On Wed, Oct 15, 2025 at 05:30:07PM +0200, Loïc Molinari wrote:

This looks fine, no need to resend to fix this, but if you'd written
the previous patch slightly differently, you'd've reduced the amount of
code you moved around in this patch, which would have made it easier to
review.

> +	/* Map a range of pages around the faulty address. */
> +	do {
> +		pfn = page_to_pfn(pages[start_pgoff]);
> +		ret = vmf_insert_pfn(vma, addr, pfn);
> +		addr += PAGE_SIZE;
> +	} while (++start_pgoff <= end_pgoff && ret == VM_FAULT_NOPAGE);

It looks to me like we have an opportunity to do better here by
adding a vmf_insert_pfns() interface.  I don't think we should delay
your patch series to add it, but let's not forget to do that; it can
have very good performnce effects on ARM to use contptes.

> @@ -617,8 +645,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
[...]
>  
> -		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
> +	if (drm_gem_shmem_map_pmd(vmf, vmf->address, pages[page_offset])) {
> +		ret = VM_FAULT_NOPAGE;
> +		goto out;
>  	}

Does this actually work?