linux-kernel - Re: [PATCH] 9p/virtio: restrict page pinning to user_backed

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Message-ID: <815091.1766145812@warthog.procyon.org.uk>
Date: Fri, 19 Dec 2025 12:03:32 +0000
From: David Howells <dhowells@...hat.com>
To: Dominique Martinet <asmadeus@...ewreck.org>
Cc: dhowells@...hat.com, Christoph Hellwig <hch@...radead.org>,
    Eric Van Hensbergen <ericvh@...nel.org>,
    Latchesar Ionkov <lucho@...kov.net>,
    Christian Schoenebeck <linux_oss@...debyte.com>,
    v9fs@...ts.linux.dev, linux-kernel@...r.kernel.org,
    Matthew Wilcox <willy@...radead.org>, linux-fsdevel@...r.kernel.org,
    Chris Arges <carges@...udflare.com>
Subject: Re: [PATCH] 9p/virtio: restrict page pinning to user_backed_iter() iovec

Dominique Martinet <asmadeus@...ewreck.org> wrote:

> FWIW I tried logging and saw ITER_BVEC, ITER_KVEC and ITER_FOLIOQ --
> O_DIRECT writes are seen as BVEC so I guess it's not as direct as I
> expected them to be -- that code could very well be leftovers from
> the switch to iov_iter back in 2015...

ITER_FOLIOQ should only be seen from buffered I/O.  For unbuffered/direct I/O,
user-backed writes are extracted to ITER_BVEC; kernel-backed writes are
sliced, but the original iter type comes down.  For the moment.

David