linux-kernel - Re: [PATCH v3 4/9] drm/rockchip/rockchip_drm_gem.c: Convert to use vm_insert

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Message-ID: <CAFqt6zbMbvB1ckwhSsBATrq5M-HQ6qk95sCWCoTTFFnwzBAnng@mail.gmail.com>
Date:   Sat, 8 Dec 2018 02:00:36 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     robin.murphy@....com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>, hjc@...k-chips.com,
        Heiko Stuebner <heiko@...ech.de>, airlied@...ux.ie,
        Linux-MM <linux-mm@...ck.org>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 4/9] drm/rockchip/rockchip_drm_gem.c: Convert to use vm_insert_range

On Fri, Dec 7, 2018 at 8:20 PM Robin Murphy <robin.murphy@....com> 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@...il.com>
> > Tested-by: Heiko Stuebner <heiko@...ech.de>
> > Acked-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >   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 ?