Date:   Sat, 6 Jan 2018 22:02:31 +0200
From:   Alexander Kapshuk <alexander.kapshuk@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, michael.thayer@...cle.com,
        dri-devel@...ts.freedesktop.org, peda@...ntia.se,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Cihangir Aktürk <cakturk@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

On Sat, Jan 6, 2018 at 10:00 PM, Hans de Goede <hdegoede@...hat.com> wrote:
> Hi,
>
>
> On 06-01-18 20:56, Alexander Kapshuk wrote:
>>
>> On Sat, Jan 6, 2018 at 9:43 PM, Hans de Goede <hdegoede@...hat.com> wrote:
>>>
>>> HI,
>>>
>>>
>>> On 06-01-18 20:30, Alexander Kapshuk wrote:
>>>>
>>>>
>>>> On Sat, Jan 6, 2018 at 6:00 PM, Hans de Goede <hdegoede@...hat.com>
>>>> 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@...il.com>
>>>>>>> ---
>>>>>>>     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

Understood.
Thanks.

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