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

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Date:   Sat, 6 Jan 2018 21:00:49 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Alexander Kapshuk <alexander.kapshuk@...il.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

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