[Intel-gfx] [PATCH 01/13] video: fb_defio: preserve user fb_ops
Daniel Vetter
daniel at ffwll.ch
Thu Nov 28 10:08:09 UTC 2019
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.
-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
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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