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

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Message-ID: <YTDjlixwDWi7Y2uR@phenom.ffwll.local>
Date:   Thu, 2 Sep 2021 16:45:42 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Anton Ivanov <anton.ivanov@...bridgegreys.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        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, Sep 02, 2021 at 07:19:01AM +0100, Anton Ivanov wrote:
> On 02/09/2021 06:52, Randy Dunlap wrote:
> > On 9/1/21 10:48 PM, Anton Ivanov wrote:
> > > On 02/09/2021 03:01, Randy Dunlap wrote:
> > > > boot_cpu_data [struct cpuinfo_um (on UML)] does not have a struct
> > > > member named 'x86', so provide a default page protection mode
> > > > for CONFIG_UML.
> > > > 
> > > > Mends this build error:
> > > > ../drivers/gpu/drm/ttm/ttm_module.c: In function
> > > > ‘ttm_prot_from_caching’:
> > > > ../drivers/gpu/drm/ttm/ttm_module.c:59:24: error: ‘struct
> > > > cpuinfo_um’ has no member named ‘x86’
> > > >    else if (boot_cpu_data.x86 > 3)
> > > >                          ^
> > > > 
> > > > Fixes: 3bf3710e3718 ("drm/ttm: Add a generic TTM memcpy move for
> > > > page-based iomem")
> > > > Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> > > > Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> > > > Cc: Christian König <christian.koenig@....com>
> > > > Cc: Huang Rui <ray.huang@....com>
> > > > Cc: dri-devel@...ts.freedesktop.org
> > > > Cc: Jeff Dike <jdike@...toit.com>
> > > > Cc: Richard Weinberger <richard@....at>
> > > > Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> > > > Cc: linux-um@...ts.infradead.org
> > > > Cc: David Airlie <airlied@...ux.ie>
> > > > Cc: Daniel Vetter <daniel@...ll.ch>
> > > > ---
> > > >   drivers/gpu/drm/ttm/ttm_module.c |    4 ++++
> > > >   1 file changed, 4 insertions(+)
> > > > 
> > > > --- linux-next-20210901.orig/drivers/gpu/drm/ttm/ttm_module.c
> > > > +++ linux-next-20210901/drivers/gpu/drm/ttm/ttm_module.c
> > > > @@ -53,6 +53,9 @@ pgprot_t ttm_prot_from_caching(enum ttm_
> > > >       if (caching == ttm_cached)
> > > >           return tmp;
> > > > +#ifdef CONFIG_UML
> > > > +    tmp = pgprot_noncached(tmp);
> > > > +#else
> > > >   #if defined(__i386__) || defined(__x86_64__)
> > > >       if (caching == ttm_write_combined)
> > > >           tmp = pgprot_writecombine(tmp);
> > > > @@ -69,6 +72,7 @@ pgprot_t ttm_prot_from_caching(enum ttm_
> > > >   #if defined(__sparc__)
> > > >       tmp = pgprot_noncached(tmp);
> > > >   #endif
> > > > +#endif
> > > >       return tmp;
> > > >   }
> > > 
> > > Patch looks OK.
> > > 
> > > 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.

I thought kunit is based on top of uml, and we do want to eventually adopt
that. Especially for helper libraries like ttm.

But also that's quite a bit in the future.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch