linux-kernel - Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap

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Message-ID: <87pn4zl2ia.fsf@nanos.tec.linutronix.de>
Date:   Sat, 31 Oct 2020 00:26:05 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...nel.org>,
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        Daniel Vetter <daniel@...ll.ch>,
        Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Christoph Hellwig <hch@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
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        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends

On Fri, Oct 30 2020 at 15:46, Linus Torvalds wrote:
> On Fri, Oct 30, 2020 at 3:26 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> To me, your patch series has two big advantages:
>
>  - more common code
>
>  - kmap_local() becomes more of a no-op
>
> and the last thing we want is to expand on kmap.

Happy to go with that.

While trying to document the mess, I just stumbled over the abuse of
kmap_atomic_prot() in

drivers/gpu/drm/ttm/ttm_bo_util.c:      dst = kmap_atomic_prot(d, prot);
drivers/gpu/drm/ttm/ttm_bo_util.c:      src = kmap_atomic_prot(s, prot);
drivers/gpu/drm/vmwgfx/vmwgfx_blit.c:   kmap_atomic_prot(d->dst_pages[dst_page],
drivers/gpu/drm/vmwgfx/vmwgfx_blit.c:   kmap_atomic_prot(d->src_pages[src_page],

For !HIGHMEM kmap_atomic_prot() just ignores the 'prot' argument and
returns the page address. 

Moar patches to be written ... Sigh!

Thanks,

        tglx