linux-kernel - Re: [PATCH v7] Add udmabuf misc device

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Date:   Mon, 10 Sep 2018 19:39:20 +0200
From:   Gert Wollny <gert.wollny@...labora.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v7] Add udmabuf misc device

Using the kernel 4.19.0-rc2 it works now, so With the fix for not
calling fput when memfd == NULL the patch is 
  Reviewed-By: Gert Wollny <gert.wollny@...labora.com>

best,
Gert 

Am Montag, den 10.09.2018, 15:30 +0200 schrieb Gerd Hoffmann:
> On Mon, Sep 10, 2018 at 01:31:08PM +0200, Gert Wollny wrote:
> > Am Montag, den 10.09.2018, 12:53 +0200 schrieb Gerd Hoffmann:
> > > 
> > > By default qemu doesn't use memfd for backing storage, you have
> > > to
> > > explicitly configure qemu that way (see qemu commit log of the
> > > test
> > > branch):
> > > 
> > >     qemu-system-x86_64 -m 2G
> > >             -object memory-backend-memfd,id=ram,size=2G
> > >             -numa node,memdev=ram"
> > 
> > Thanks, but that doesn't seem to help.
> 
> Note the memory is specified twice, once with -m, once for the
> memory-backend-memfd object.  The two must match of course (or, to be
> exact, the sum of all memory backends must match the total memory,
> but
> unless you want create a virtual numa machine there is no reason to
> have
> multiple memory-backends).
> 
> > Are there any host kernel
> > configuration parameters or features that I should set (apart from
> > enabling udmabuf)? 
> 
> I'm not aware of any unusual parameters required.  My config is based
> on
> rhel-7, then stripped down with localmodconfig, then enabled the bits
> I
> want in my test kernel.
> 
> Oh, wait, CONFIG_MEMFD_CREATE could be the one.  I guess I should add
> a
> Kconfig dependency.  Even though udmabuf will build just fine without
> that (because memfd is basically shmem with some features on top) it
> doesn't buy you much if the memfd_create syscall is not available ...
> 
> cheers,
>   Gerd
>