linux-kernel - Re: [PATCH 2/7] xen/gntdev,x86: Remove apply_to_page

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Message-ID: <YHQQ7YsBbtXl0+Ml@hirez.programming.kicks-ass.net>
Date:   Mon, 12 Apr 2021 11:20:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@....de>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, x86@...nel.org,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, chris@...is-wilson.co.uk,
        intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
        keescook@...omium.org
Subject: Re: [PATCH 2/7] xen/gntdev,x86: Remove apply_to_page_range() use
 from module

On Mon, Apr 12, 2021 at 10:26:40AM +0200, Christoph Hellwig wrote:
> On Mon, Apr 12, 2021 at 10:00:14AM +0200, Peter Zijlstra wrote:
> > Instead of relying on apply_to_page_range() being available to
> > modules, move its use into core kernel code and export it's
> > application.
> 
> This doesn't exactly look great, but at least it contains the damage..

That was just about as far as I got...

> > NOTE: ideally we do: use_ptemod = !auto_translate_physmap &&
> > gnttab_map_avail_bits and remove this hack.
> 
> Given how much pain the !auto_translate_physmap case causes all over
> the kernel I wonder what a realistic timeline might be for dropping
> support for this case might be..

I've no experience with any of that; it looks absolutely disguisting,
all of it. I figured that's part of the Xen 'charm' :-)