[Intel-gfx] [PATCH 01/13] video: fb_defio: preserve user fb_ops
Jani Nikula
jani.nikula at intel.com
Thu Nov 28 10:34:40 UTC 2019
On Thu, 28 Nov 2019, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Thu, Nov 28, 2019 at 11:05:57AM +0100, Daniel Vetter wrote:
>> On Thu, Nov 28, 2019 at 11:09:46AM +0200, Jani Nikula wrote:
>> > On Wed, 27 Nov 2019, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > > On Wed, Nov 27, 2019 at 07:17:41PM +0100, Daniel Vetter wrote:
>> > >> On Wed, Nov 27, 2019 at 06:31:57PM +0200, Jani Nikula wrote:
>> > >> > Modifying fb_ops directly to override fb_mmap with fb_deferred_io_mmap
>> > >> > and then resetting it to NULL afterwards causes problems all over the
>> > >> > place. First, it prevents making the fbops member of struct fb_info a
>> > >> > const pointer, which means we can't make struct fb_ops const
>> > >> > anywhere. Second, a few places have to go out of their way to restore
>> > >> > the original fb_mmap pointer that gets reset to NULL.
>> > >> >
>> > >> > Preserve the passed in fb_ops by making a copy of it and modifying that
>> > >> > instead. Add a deferred_io_private member to struct fb_info to store the
>> > >> > pointer to the old fb_ops, and restore that at cleanup.
>> > >> >
>> > >> > Cc: Jaya Kumar <jayalk at intworks.biz>
>> > >> > Cc: linux-fbdev at vger.kernel.org
>> > >> > Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>> > >> >
>> > >> > ---
>> > >> >
>> > >> > Note: If the approach is acceptable, we'll also need to handle the error
>> > >> > returns on memory allocation failures at fb_deferred_io_init() call
>> > >> > sites. There are 13.
>> > >>
>> > >> it's fbdev defio, I think we can do worse with less effort. Just embed a
>> > >> copy of fb_ops into fb_info, and use that, and tada! no memory allocation
>> > >> needed :-)
>> > >>
>> > >> I'd totally r-b that patch.
>> > >>
>> > >> Or do what Ville suggested, add an fb_info->fbdefio.enabled, set that in
>> > >> the _init function and in fb_mmap call fb_deferred_io_mmap for that case
>> > >> instead of the driver's fb_ops->fb_mmap. There's only one caller of that
>> > >> in the entire tree, in fbmem.c. Also, we could/should nuke the
>> > >> EXPORT_SYMBOL(fb_deferred_io_mmap) I think.
>> > >
>> > > I just realized that fb_info->fbdefio is a pointer, so this would be
>> > > really simple to pull off I think.
>> >
>> > Heh, having a
>> >
>> > int (*fb_deferred_io_mmap)(struct fb_info *, struct vm_area_struct *);
>> >
>> > member in struct fb_info, and using that in fbmem.c if non-NULL, was
>> > actually my first idea. I didn't think it was particularly pretty, but
>> > if we don't care about aesthetics...
>> >
>> > Would you like that instead of the patch at hand?
>>
>>
>> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
>> index 82c20c6047b0..9275c6bd71da 100644
>> --- a/drivers/video/fbdev/core/fb_defio.c
>> +++ b/drivers/video/fbdev/core/fb_defio.c
>> @@ -206,13 +206,11 @@ void fb_deferred_io_init(struct fb_info *info)
>>
>> BUG_ON(!fbdefio);
>> mutex_init(&fbdefio->lock);
>> - info->fbops->fb_mmap = fb_deferred_io_mmap;
>> INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work);
>> INIT_LIST_HEAD(&fbdefio->pagelist);
>> if (fbdefio->delay == 0) /* set a default of 1 s */
>> fbdefio->delay = HZ;
>> }
>> -EXPORT_SYMBOL_GPL(fb_deferred_io_init);
>>
>> void fb_deferred_io_open(struct fb_info *info,
>> struct inode *inode,
>> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
>> index 86b06a599f96..6af627f281c3 100644
>> --- a/drivers/video/fbdev/core/fbmem.c
>> +++ b/drivers/video/fbdev/core/fbmem.c
>> @@ -1341,7 +1341,16 @@ fb_mmap(struct file *file, struct vm_area_struct * vma)
>> return -ENODEV;
>> fb = info->fbops;
>> mutex_lock(&info->mm_lock);
>> - if (fb->fb_mmap) {
>> + if (fb->fbdefio) {
>> + /*
>> + * The framebuffer needs to be accessed decrypted, be sure
>> + * SME protection is removed ahead of the call
>> + */
>> + vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
>> + res = fb_deferred_io_mmap(info, vma);
>> + mutex_unlock(&info->mm_lock);
>> + return res;
>> + } else if (fb->fb_mmap) {
>> int res;
>>
>> /*
>>
>> Is what I was thinking off as the pretty solution. Add an explicit
>> fb_info->fbdefio_enabled boolean if you don't feel like auditing all the
>> drivers for whether they really call defio_init() every time they assign
>> something to that pointer. A quick scan brought some nasties to light in
>> that area.
>
> Correction, brain wasn't awake yet, I've done the audit and the above diff
> should work afaict.
It just felt sketchy to me to depend on that pointer being set as the
decider, independent of defio init. But if you think that's the way to
go, I'm not going to argue. I'll bet it won't go unnoticed if
fb_deferred_io_mmap() gets called without the init. ;)
BR,
Jani.
> -Daniel
>
>>
>> I think a function pointer here is pointless because we clearly don't need
>> it, and with all the panic around function pointers a direct call feels
>> much better :-)
>> -Daniel
>>
>> >
>> > BR,
>> > Jani.
>> >
>> >
>> > > -Daniel
>> > >
>> > >>
>> > >> That version would also get my r-b stamp. So up to you what you prefer.
>> > >> -Daniel
>> > >>
>> > >> > ---
>> > >> > drivers/video/fbdev/core/fb_defio.c | 25 ++++++++++++++++++++++---
>> > >> > include/linux/fb.h | 3 ++-
>> > >> > 2 files changed, 24 insertions(+), 4 deletions(-)
>> > >> >
>> > >> > diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
>> > >> > index 82c20c6047b0..36697844c1e0 100644
>> > >> > --- a/drivers/video/fbdev/core/fb_defio.c
>> > >> > +++ b/drivers/video/fbdev/core/fb_defio.c
>> > >> > @@ -200,13 +200,23 @@ static void fb_deferred_io_work(struct work_struct *work)
>> > >> > mutex_unlock(&fbdefio->lock);
>> > >> > }
>> > >> >
>> > >> > -void fb_deferred_io_init(struct fb_info *info)
>> > >> > +int fb_deferred_io_init(struct fb_info *info)
>> > >> > {
>> > >> > struct fb_deferred_io *fbdefio = info->fbdefio;
>> > >> > + struct fb_ops *fbops;
>> > >> >
>> > >> > BUG_ON(!fbdefio);
>> > >> > +
>> > >> > + fbops = kmemdup(info->fbops, sizeof(*fbops), GFP_KERNEL);
>> > >> > + if (!fbops)
>> > >> > + return -ENOMEM;
>> > >> > +
>> > >> > + fbops->fb_mmap = fb_deferred_io_mmap;
>> > >> > + info->deferred_io_private = info->fbops;
>> > >> > + info->fbops = fbops;
>> > >> > +
>> > >> > mutex_init(&fbdefio->lock);
>> > >> > - info->fbops->fb_mmap = fb_deferred_io_mmap;
>> > >> > +
>> > >> > INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work);
>> > >> > INIT_LIST_HEAD(&fbdefio->pagelist);
>> > >> > if (fbdefio->delay == 0) /* set a default of 1 s */
>> > >> > @@ -229,6 +239,12 @@ void fb_deferred_io_cleanup(struct fb_info *info)
>> > >> > int i;
>> > >> >
>> > >> > BUG_ON(!fbdefio);
>> > >> > +
>> > >> > + /* sanity check against misuse */
>> > >> > + if (WARN_ON(!info->deferred_io_private ||
>> > >> > + info->fbops->fb_mmap != fb_deferred_io_mmap))
>> > >> > + return;
>> > >> > +
>> > >> > cancel_delayed_work_sync(&info->deferred_work);
>> > >> >
>> > >> > /* clear out the mapping that we setup */
>> > >> > @@ -237,7 +253,10 @@ void fb_deferred_io_cleanup(struct fb_info *info)
>> > >> > page->mapping = NULL;
>> > >> > }
>> > >> >
>> > >> > - info->fbops->fb_mmap = NULL;
>> > >> > + kfree(info->fbops);
>> > >> > + info->fbops = info->deferred_io_private;
>> > >> > + info->deferred_io_private = NULL;
>> > >> > +
>> > >> > mutex_destroy(&fbdefio->lock);
>> > >> > }
>> > >> > EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
>> > >> > diff --git a/include/linux/fb.h b/include/linux/fb.h
>> > >> > index a6ad528990de..65f2abd47745 100644
>> > >> > --- a/include/linux/fb.h
>> > >> > +++ b/include/linux/fb.h
>> > >> > @@ -470,6 +470,7 @@ struct fb_info {
>> > >> > #ifdef CONFIG_FB_DEFERRED_IO
>> > >> > struct delayed_work deferred_work;
>> > >> > struct fb_deferred_io *fbdefio;
>> > >> > + void *deferred_io_private;
>> > >> > #endif
>> > >> >
>> > >> > struct fb_ops *fbops;
>> > >> > @@ -658,7 +659,7 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
>> > >> >
>> > >> > /* drivers/video/fb_defio.c */
>> > >> > int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
>> > >> > -extern void fb_deferred_io_init(struct fb_info *info);
>> > >> > +extern int fb_deferred_io_init(struct fb_info *info);
>> > >> > extern void fb_deferred_io_open(struct fb_info *info,
>> > >> > struct inode *inode,
>> > >> > struct file *file);
>> > >> > --
>> > >> > 2.20.1
>> > >> >
>> > >> > _______________________________________________
>> > >> > Intel-gfx mailing list
>> > >> > Intel-gfx at lists.freedesktop.org
>> > >> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>> > >>
>> > >> --
>> > >> Daniel Vetter
>> > >> Software Engineer, Intel Corporation
>> > >> http://blog.ffwll.ch
>> >
>> > --
>> > Jani Nikula, Intel Open Source Graphics Center
>>
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch
--
Jani Nikula, Intel Open Source Graphics Center
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