linux-kernel - Re: [PATCH] mm/highmem: Align-down to page the address for kunmap_flush_on

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Date:   Fri, 27 Jan 2023 18:58:55 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        David Sterba <dsterba@...e.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Al Viro <viro@...iv.linux.org.uk>, Helge Deller <deller@....de>
Subject: Re: [PATCH] mm/highmem: Align-down to page the address for
 kunmap_flush_on_unmap()

On giovedì 26 gennaio 2023 21:07:53 CET Matthew Wilcox wrote:
> On Thu, Jan 26, 2023 at 03:33:46PM +0100, Fabio M. De Francesco wrote:
> > If ARCH_HAS_FLUSH_ON_KUNMAP is defined (PA-RISC case), __kunmap_local()
> > calls kunmap_flush_on_unmap(). The latter currently flushes the wrong
> > address (as confirmed by Matthew Wilcox and Helge Deller). Al Viro
> > proposed to call kunmap_flush_on_unmap() on an aligned-down to page
> > address in order to fix this issue. Consensus has been reached on this
> > solution.
> > 
> > Therefore, if ARCH_HAS_FLUSH_ON_KUNMAP is defined, call
> > kunmap_flush_on_unmap() on an aligned-down to page address computed with
> > the PTR_ALIGN_DOWN() macro.
> 
> You missed a spot.  Sent the version I've had in my tree for a few days.

I'm sorry for missing the other call site.
Furthermore, your patch has a better commit message. 

However, I'm also sorry because I would have expected a different kind of 
support from you. My patch could have been improved with v2.

Anyway, I assume that you missed that I had asked you and Al if anybody were 
interested in doing these changes and probably you missed also that Ira 
encouraged me to send a patch, whereas you did not show any interest...
https://lore.kernel.org/lkml/3146373.5fSG56mABF@suse/

Fabio

P.S.: Helge wrote to me privately but you cannot know it.