linux-kernel - Re: [PATCH] highmem: fix highmem for xtensa

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Date:   Fri, 13 Nov 2020 05:50:57 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>, Chris Zankel <chris@...kel.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] highmem: fix highmem for xtensa

Hi Thomas,

On Fri, Nov 13, 2020 at 5:40 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> On Fri, Nov 13 2020 at 04:23, Max Filippov wrote:
> > Fixmap on xtensa grows upwards, i.e. bigger fixmap entry index
> > corresponds to a higher virtual address. This was lost in highmem
> > generalization resulting in the following runtime warnings:
>
> Sorry for not noticing.
>
> > Fix it by adding __ARCH_HAS_POSITIVE_FIXMAP macro and implementing
> > vaddr_in_fixmap and fixmap_pte primitives differently depending on
> > whether it is defined or not.
>
> What's wrong with just doing the obvious and making the fixmap defines
> the other way round?

It becomes really awkward when we get to support high memory with
aliasing data cache: we must think about the actual virtual addresses
assigned to pages and it feels much simpler when it's done this way.

-- 
Thanks.
-- Max