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

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Message-ID: <20190830111605.twzssycagmjhfa45@sirius.home.kraxel.org>
Date:   Fri, 30 Aug 2019 13:16:05 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     David Riley <davidriley@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Stéphane Marchesin <marcheu@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/virtio: Use vmalloc for command buffer allocations.

  Hi,

> > > -     kfree(vbuf->data_buf);
> > > +     kvfree(vbuf->data_buf);
> >
> > if (is_vmalloc_addr(vbuf->data_buf)) ...
> >
> > needed here I gues?
> >
> 
> kvfree() handles vmalloc/kmalloc/kvmalloc internally by doing that check.

Ok.

> - videobuf_vmalloc_to_sg in drivers/media/v4l2-core/videobuf-dma-sg.c,
> assumes contiguous array of scatterlist and that the buffer being converted
> is page aligned

Well, vmalloc memory _is_ page aligned.

sg_alloc_table_from_pages() does alot of what you need, you just need a
small loop around vmalloc_to_page() create a struct page array
beforehand.

Completely different approach: use get_user_pages() and don't copy the
execbuffer at all.

cheers,
  Gerd