linux-kernel - Re: [PATCH V2] highmem: Fix kmap_to_page() for kmap_local

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Message-Id: <20221006133331.dabd345508f7d62a887dfb4d@linux-foundation.org>
Date:   Thu, 6 Oct 2022 13:33:31 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     ira.weiny@...el.com
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        kernel test robot <lkp@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] highmem: Fix kmap_to_page() for kmap_local_page()
 addresses

On Wed,  5 Oct 2022 21:05:55 -0700 ira.weiny@...el.com wrote:

> kmap_to_page() is used to get the page for a virtual address which may
> be kmap'ed.  Unfortunately, kmap_local_page() stores mappings in a
> thread local array separate from kmap().  These mappings were not
> checked by the call.
> 
> Check the kmap_local_page() mappings and return the page if found.
> 
> Because it is intended to remove kmap_to_page() add a warn on once to
> the kmap checks to flag potential issues early.

What were the user-visible runtime effects of this?

Are we able to identify a Fixes:?

Thanks.