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

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Date:   Mon, 12 Apr 2021 11:26:59 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Christoph Hellwig <hch@....de>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.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 12.04.21 10:26, 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..
> 
>>
>> 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..

Think in the order of years.

It is basically the Xen PV guest support you are speaking of here, and
the planned replacement PVH especially for dom0 is still lacking some
functionality and it has performance issues.


Juergen

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