linux-ext4 - Re: [REGRESSION] Re: [PATCH v8 15/19] mm: don't allow huge faults for files with pre content watches

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Message-ID: <CAHk-=wi2pThSVY=zhO=ZKxViBj5QCRX-=AS2+rVknQgJnHXDFg@mail.gmail.com>
Date: Sat, 1 Feb 2025 16:58:26 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Christian Brauner <brauner@...nel.org>
Cc: Peter Xu <peterx@...hat.com>, Alex Williamson <alex.williamson@...hat.com>, 
	Josef Bacik <josef@...icpanda.com>, kernel-team@...com, linux-fsdevel@...r.kernel.org, 
	jack@...e.cz, amir73il@...il.com, viro@...iv.linux.org.uk, 
	linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-mm@...ck.org, 
	linux-ext4@...r.kernel.org, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [REGRESSION] Re: [PATCH v8 15/19] mm: don't allow huge faults for
 files with pre content watches

On Sat, 1 Feb 2025 at 06:38, Christian Brauner <brauner@...nel.org> wrote:
>
> Ok, but those "device fds" aren't really device fds in the sense that
> they are character fds. They are regular files afaict from:
>
> vfio_device_open_file(struct vfio_device *device)
>
> (Well, it's actually worse as anon_inode_getfile() files don't have any
> mode at all but that's beside the point.)?
>
> In any case, I think you're right that such files would (accidently?)
> qualify for content watches afaict. So at least that should probably get
> FMODE_NONOTIFY.

Hmm. Can we just make all anon_inodes do that? I don't think you can
sanely have pre-content watches on anon-inodes, since you can't really
have access to them to _set_ the content watch from outside anyway..

In fact, maybe do it in alloc_file_pseudo()?

Amir / Josef?

              Linus