linux-kernel - Re: [PATCH] vboxsf: Convert vboxsf_write_end() to use kmap_local

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Message-ID: <CAKha_srnh8HOMdHPp1Dd9drMhtM+oROvC3UDx+N2wiFvwDe-YA@mail.gmail.com>
Date: Tue, 12 Aug 2025 01:29:34 +0300
From: Tal Zussman <tz2294@...umbia.edu>
To: Matthew Wilcox <willy@...radead.org>
Cc: Hans de Goede <hansg@...nel.org>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vboxsf: Convert vboxsf_write_end() to use kmap_local_folio()

On Tue, Aug 12, 2025 at 1:12 AM Matthew Wilcox <willy@...radead.org> wrote:
> On Mon, Aug 11, 2025 at 05:42:00PM -0400, Tal Zussman wrote:
> > Now that vboxsf_write_end() takes a folio, convert the kmap() call to
> > kmap_local_folio(). This removes two instances of &folio->page as
> > well.
> >
> > Compile-tested only.
>
> Yeah ... I don't know if this is safe or not.  Needs actual testing.

Could you elaborate on why this might be unsafe? I assumed that (1) this is
similar to the conversion done in vboxsf_writepages() and (2) that the
kmap() call here could be simply converted to kmap_local_page() and then to
kmap_local_folio(), but clearly I'm missing something...