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Date:   Thu, 13 Jul 2023 14:46:17 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        Wang Yugui <wangyugui@e16-tech.com>,
        Dave Chinner <david@fromorbit.com>,
        Christoph Hellwig <hch@infradead.org>,
        Kent Overstreet <kent.overstreet@linux.dev>
Subject: Re: [PATCH v4 1/9] iov_iter: Handle compound highmem pages in
 copy_page_from_iter_atomic()
Message-ID: <ZLAAKSZ0wXP54AfF@casper.infradead.org>
References: <20230710130253.3484695-1-willy@infradead.org>
 <20230710130253.3484695-2-willy@infradead.org>
 <20230713044207.GH108251@frogsfrogsfrogs>
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On Wed, Jul 12, 2023 at 09:42:07PM -0700, Darrick J. Wong wrote:
> On Mon, Jul 10, 2023 at 02:02:45PM +0100, Matthew Wilcox (Oracle) wrote:
> > copy_page_from_iter_atomic() already handles !highmem compound
> > pages correctly, but if we are passed a highmem compound page,
> > each base page needs to be mapped & unmapped individually.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> Yikes.  Does this want a fixes tag?

I was wondering the same thing.  I think the bug is merely latent,
and all existing users limit themselves to being within the page
that they're passing in.