linux-kernel - Re: [PATCH] drm/virtio: Use vmalloc for command buffer allocations.

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Message-ID: <20190902051921.nczclnaqcmxlh7bz@sirius.home.kraxel.org>
Date:   Mon, 2 Sep 2019 07:19:21 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Chia-I Wu <olvaffe@...il.com>
Cc:     David Riley <davidriley@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Stéphane Marchesin <marcheu@...omium.org>,
        "open list:VIRTIO CORE, NET AND BLOCK DRIVERS" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH] drm/virtio: Use vmalloc for command buffer allocations.

> > Completely different approach: use get_user_pages() and don't copy the
> > execbuffer at all.
> It would be really nice if execbuffer does not copy.
> 
> The user space owns the buffer and may overwrite the contents
> immediately after the ioctl.

Oh, right.  The exec ioctl doesn't block.  So this doesn't work (breaks
userspace abi).  Scratch the idea then.

> We also need a flag to indicate that the
> ownership of the buffer is transferred to the kernel.

Yes, with an additional flag for the changed behavior it could work.

cheers,
  Gerd