Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

[Hans de Goede]

Hi,

On 06-01-18 20:56, Alexander Kapshuk wrote:
> On Sat, Jan 6, 2018 at 9:43 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > HI,
> >
> >
> > On 06-01-18 20:30, Alexander Kapshuk wrote:
> > > On Sat, Jan 6, 2018 at 6:00 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > > > Hi,
> > > >
> > > >
> > > > On 06-01-18 15:20, Alexander Kapshuk wrote:
> > > > > On Mon, Dec 25, 2017 at 04:42:59PM +0200, Alexander Kapshuk wrote:
> > > > > > Sparse emitted the following warning:
> > > > > > ../drivers/staging/vboxvideo/vbox_fb.c:173:27: warning: incorrect type
> > > > > > in
> > > > > > assignment (different address spaces)
> > > > > > ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    expected char
> > > > > > [noderef]
> > > > > > <asn:2>*screen_base
> > > > > > ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    got void *virtual
> > > > > >
> > > > > > The vbox_bo buffer object kernel mapping is handled by a call
> > > > > > to ttm_bo_kmap() prior to the assignment of bo->kmap.virtual to
> > > > > > info->screen_base of type char __iomem*.
> > > > > > Casting bo->kmap.virtual to char __iomem* in this assignment fixes
> > > > > > the warning.
> > > > > >
> > > > > > vboxvideo: Fix address space of expression removal sparse warning
> > > > > >
> > > > > > Sparse emitted the following warning:
> > > > > > ../drivers/staging/vboxvideo/vbox_main.c:64:25: warning: cast removes
> > > > > > address space of expression
> > > > > >
> > > > > > vbox->vbva_buffers iomapping is handled by calling vbox_accel_init()
> > > > > > from vbox_hw_init().
> > > > > > __force attribute is used in assignment to vbva to fix the warning.
> > > > > >
> > > > > > Signed-off-by: Alexander Kapshuk <alexander.kapshuk@xxxxxxxxx>
> > > > > > ---
> > > > > >     drivers/staging/vboxvideo/vbox_fb.c   | 2 +-
> > > > > >     drivers/staging/vboxvideo/vbox_main.c | 2 +-
> > > > > >     2 files changed, 2 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/staging/vboxvideo/vbox_fb.c
> > > > > > b/drivers/staging/vboxvideo/vbox_fb.c
> > > > > > index 8aed248db6e2..43c39eca4ae1 100644
> > > > > > --- a/drivers/staging/vboxvideo/vbox_fb.c
> > > > > > +++ b/drivers/staging/vboxvideo/vbox_fb.c
> > > > > > @@ -170,7 +170,7 @@ static int vboxfb_create(struct drm_fb_helper
> > > > > > *helper,
> > > > > >           drm_fb_helper_fill_var(info, &fbdev->helper, sizes->fb_width,
> > > > > >                                  sizes->fb_height);
> > > > > >
> > > > > > -       info->screen_base = bo->kmap.virtual;
> > > > > > +       info->screen_base = (char __iomem *)bo->kmap.virtual;
> > > > > >           info->screen_size = size;
> > > > > >
> > > > > >     #ifdef CONFIG_DRM_KMS_FB_HELPER
> > > >
> > > >
> > > >
> > > > This fix looks good to me.
> > > >
> > > > > > diff --git a/drivers/staging/vboxvideo/vbox_main.c
> > > > > > b/drivers/staging/vboxvideo/vbox_main.c
> > > > > > index 80bd039fa08e..973b3bcc04b1 100644
> > > > > > --- a/drivers/staging/vboxvideo/vbox_main.c
> > > > > > +++ b/drivers/staging/vboxvideo/vbox_main.c
> > > > > > @@ -61,7 +61,7 @@ void vbox_enable_accel(struct vbox_private *vbox)
> > > > > >                   if (vbox->vbva_info[i].vbva)
> > > > > >                           continue;
> > > > > >
> > > > > > -               vbva = (void *)vbox->vbva_buffers + i *
> > > > > > VBVA_MIN_BUFFER_SIZE;
> > > > > > +               vbva = (void __force *)vbox->vbva_buffers + i *
> > > > > > VBVA_MIN_BUFFER_SIZE;
> > > > > >                   if (!vbva_enable(&vbox->vbva_info[i],
> > > > > >                                    vbox->guest_pool, vbva, i)) {
> > > > > >                           /* very old host or driver error. */
> > > >
> > > >
> > > >
> > > > Hmm, isn't there a cleaner way to fix this ? Maybe make vbva_enable's
> > > > argument (and the local vbva variable) of type u8 __iomem * too ?
> > > >
> > > > Regards,
> > > >
> > > > Hans
> > >
> > >
> > > Hi Hans,
> > >
> > > Thanks for your prompt response.
> > >
> > > I had a good look at the vbva_enable() function's definition and to
> > > the best of my knowledge, changing vbva's type from 'struct
> > > vbva_buffer *' to 'u8 __iomem *' wouldn't work.
> > > vbva_enable() relies on vbva's type being a pointer to 'struct
> > > vbva_buffer':
> > > vbva's memory gets set to zero;
> > > some of vbva's members are initialised to particular values;
> > > vbva_ctx->vbva expects vbva to be a pointer to 'struct vbva_buffer' as
> > > well;
> > >
> > > Or am I misreading this?
> >
> >
> > No your not misreading this I did not check the function myself before
> > commenting myself, my bad.
>
> Thanks for confirming my understanding of this.
>
> > > What are your thoughts on this?
> >
> >
> > Lets just move ahead with your original fix:
>
> Did you want me to resend the patch, or is someone going to pull the
> original one I sent into their tree?
> Thanks.

I expect Greg to pick it up without a resend. But with all the Spectre
stuff going on right now he might miss it, so I would say give it 14 days
and if he has not picked it up by then, resend it with my reviewed-by
added.

Regards,

Hans