Re: [PATCH v3 4/9] drm/rockchip/rockchip_drm_gem.c: Convert to use vm_insert_range

[Robin Murphy]

On 2018-12-07 8:30 pm, Souptick Joarder wrote:
> On Fri, Dec 7, 2018 at 8:20 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > On 06/12/2018 18:42, Souptick Joarder wrote:
> > > Convert to use vm_insert_range() to map range of kernel
> > > memory to user vma.
> > >
> > > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > > Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
> > > Acked-by: Heiko Stuebner <heiko@xxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 20 ++------------------
> > >    1 file changed, 2 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > index a8db758..2cb83bb 100644
> > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > @@ -221,26 +221,10 @@ static int rockchip_drm_gem_object_mmap_iommu(struct drm_gem_object *obj,
> > >                                              struct vm_area_struct *vma)
> > >    {
> > >        struct rockchip_gem_object *rk_obj = to_rockchip_obj(obj);
> > > -     unsigned int i, count = obj->size >> PAGE_SHIFT;
> > >        unsigned long user_count = vma_pages(vma);
> > > -     unsigned long uaddr = vma->vm_start;
> > > -     unsigned long offset = vma->vm_pgoff;
> > > -     unsigned long end = user_count + offset;
> > > -     int ret;
> > > -
> > > -     if (user_count == 0)
> > > -             return -ENXIO;
> > > -     if (end > count)
> > > -             return -ENXIO;
> > >
> > > -     for (i = offset; i < end; i++) {
> > > -             ret = vm_insert_page(vma, uaddr, rk_obj->pages[i]);
> > > -             if (ret)
> > > -                     return ret;
> > > -             uaddr += PAGE_SIZE;
> > > -     }
> > > -
> > > -     return 0;
> > > +     return vm_insert_range(vma, vma->vm_start, rk_obj->pages,
> > > +                             user_count);
> >
> > We're losing vm_pgoff handling here, which given the implication in
> > 57de50af162b, may well be a regression for at least some combination of
> > GPU and userspace driver (I assume that commit was in the context of
> > some version of the Arm Mali driver, possibly on RK3288).
>
> In commit  57de50af162b, vma->vm_pgoff = 0 for GEM mmap handler context
> and removing it from common path which means if call stack looks like
> rockchip_gem_mmap_buf() -> rockchip_drm_gem_object_mmap() ->
> rockchip_drm_gem_object_mmap_iommu(), then we might have a non zero
> vma->vm_pgoff context which is not handled.
>
> This is the problem you are pointing ? right ?

Exactly - if unconditionally zeroing the offset in the PRIME mmap() path 
was a problem, then the implication is that there are callers of that 
path who expect the offset to be honoured here.

Robin.