linux-kernel - Re: [PATCH] drm/ttm: provide default page protection for UML

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Message-ID: <c5505b203829fbcafefc9ec34cc1d7d7158c7359.camel@sipsolutions.net>
Date:   Thu, 02 Sep 2021 10:11:59 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org
Cc:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Christian König <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>, dri-devel@...ts.freedesktop.org,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        linux-um@...ts.infradead.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/ttm: provide default page protection for UML

On Thu, 2021-09-02 at 09:10 +0100, Anton Ivanov wrote:
> On 02/09/2021 08:43, Johannes Berg wrote:
> > On Thu, 2021-09-02 at 07:19 +0100, Anton Ivanov wrote:
> > > > > 
> > > > > I have a question though - why all of DRM is not !UML in config. Not
> > > > > like we can use them.
> > > > 
> > > > I have no idea about that.
> > > > Hopefully one of the (other) UML maintainers can answer you.
> > > 
> > > Touche.
> > > 
> > > We will discuss that and possibly push a patch to !UML that part of the
> > > tree. IMHO it is not applicable.
> > 
> > As I just said on the other patch, all of this is fallout from my commit
> > 68f5d3f3b654 ("um: add PCI over virtio emulation driver") which is the
> > first time that you could have PCI on UML.
> > 
> > Without having checked, in this particular case it's probably something
> > like
> > 
> > 	depends on PCI && X86_64
> > 
> > as we've seen in other drivers (idxd, ioat).
> > 
> > The biggest problem is probably that UML internally uses X86_64
> > (arch/x86/um/Kconfig), which is ... unexpected ... since CONFIG_X86_64
> > is typically considered the ARCH, and now the ARCH is actually um.
> > 
> > I think we can just fix that and get rid of this entire class of
> > problems? Something like
> > 
> > https://p.sipsolutions.net/fbac19d86637e286.txt
> 
> Good idea. I suspect that DRM will not be the only thing to pop up out 
> of this so we might as well fix it "at the top".

Yeah I sent like a handful of similar patches ...

I'll send that patch out in a minute, just writing a reasonable commit
log. Seems to build & work fine for me.

johannes