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Date:   Tue, 1 Jun 2021 15:30:30 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Nathan Chancellor <nathan@kernel.org>, linux-fbdev@vger.kernel.org,
        linux-mm@kvack.org, Jani Nikula <jani.nikula@intel.com>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        William Kucharski <william.kucharski@oracle.com>,
        Ian Campbell <ijc@hellion.org.uk>,
        linux-fsdevel@vger.kernel.org,
        Jaya Kumar <jayakumar.lkml@gmail.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2] fb_defio: Remove custom address_space_operations
Message-ID: <YLZEhv0cpZp8uVE3@casper.infradead.org>
References: <20210310185530.1053320-1-willy@infradead.org>
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 <YLY/2O16fAjriZGQ@phenom.ffwll.local>
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On Tue, Jun 01, 2021 at 04:10:32PM +0200, Daniel Vetter wrote:
> On Sun, May 30, 2021 at 10:14:22PM +0100, Matthew Wilcox wrote:
> > On Sun, May 30, 2021 at 12:13:05PM -0700, Nathan Chancellor wrote:
> > > Hi Matthew,
> > > 
> > > On Wed, Mar 10, 2021 at 06:55:30PM +0000, Matthew Wilcox (Oracle) wrote:
> > > > There's no need to give the page an address_space.  Leaving the
> > > > page->mapping as NULL will cause the VM to handle set_page_dirty()
> > > > the same way that it's handled now, and that was the only reason to
> > > > set the address_space in the first place.
> > > > 
> > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > > Reviewed-by: William Kucharski <william.kucharski@oracle.com>
> > > 
> > > This patch in mainline as commit ccf953d8f3d6 ("fb_defio: Remove custom
> > > address_space_operations") causes my Hyper-V based VM to no longer make
> > > it to a graphical environment.
> > 
> > Hi Nathan,
> > 
> > Thanks for the report.  I sent Daniel a revert patch with a full
> > explanation last week, which I assume he'll queue up for a pull soon.
> > You can just git revert ccf953d8f3d6 for yourself until that shows up.
> > Sorry for the inconvenience.
> 
> Uh that patch didn't get cc'ed to any list so I've ignored it. I've found
> it now, but lack of lore link is awkward. Can you pls resubmit with
> dri-devel on cc? fbdev list is dead, I don't look there.

How about I just attach it here?

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	filename="0001-Revert-fb_defio-Remove-custom-address_space_operatio.patch"

From e88921d0775d87323a8688af37dfd7cdebdde5a9 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Tue, 25 May 2021 08:37:33 -0400
Subject: [PATCH] Revert "fb_defio: Remove custom address_space_operations"

Commit ccf953d8f3d6 makes framebuffers which use deferred I/O stop
displaying updates after the first one.  This is because the pages
handled by fb_defio no longer have a page_mapping().  That prevents
page_mkclean() from marking the PTEs as clean, and so writes are only
noticed the first time.

Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 drivers/video/fbdev/core/fb_defio.c | 35 +++++++++++++++++++++++++++++
 drivers/video/fbdev/core/fbmem.c    |  4 ++++
 include/linux/fb.h                  |  3 +++
 3 files changed, 42 insertions(+)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index b292887a2481..a591d291b231 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -52,6 +52,13 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 
 	get_page(page);
+
+	if (vmf->vma->vm_file)
+		page->mapping = vmf->vma->vm_file->f_mapping;
+	else
+		printk(KERN_ERR "no mapping available\n");
+
+	BUG_ON(!page->mapping);
 	page->index = vmf->pgoff;
 
 	vmf->page = page;
@@ -144,6 +151,17 @@ static const struct vm_operations_struct fb_deferred_io_vm_ops = {
 	.page_mkwrite	= fb_deferred_io_mkwrite,
 };
 
+static int fb_deferred_io_set_page_dirty(struct page *page)
+{
+	if (!PageDirty(page))
+		SetPageDirty(page);
+	return 0;
+}
+
+static const struct address_space_operations fb_deferred_io_aops = {
+	.set_page_dirty = fb_deferred_io_set_page_dirty,
+};
+
 int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	vma->vm_ops = &fb_deferred_io_vm_ops;
@@ -194,12 +212,29 @@ void fb_deferred_io_init(struct fb_info *info)
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_init);
 
+void fb_deferred_io_open(struct fb_info *info,
+			 struct inode *inode,
+			 struct file *file)
+{
+	file->f_mapping->a_ops = &fb_deferred_io_aops;
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_open);
+
 void fb_deferred_io_cleanup(struct fb_info *info)
 {
 	struct fb_deferred_io *fbdefio = info->fbdefio;
+	struct page *page;
+	int i;
 
 	BUG_ON(!fbdefio);
 	cancel_delayed_work_sync(&info->deferred_work);
+
+	/* clear out the mapping that we setup */
+	for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
+		page = fb_deferred_io_page(info, i);
+		page->mapping = NULL;
+	}
+
 	mutex_destroy(&fbdefio->lock);
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 072780b0e570..98f193078c05 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1415,6 +1415,10 @@ __releases(&info->lock)
 		if (res)
 			module_put(info->fbops->owner);
 	}
+#ifdef CONFIG_FB_DEFERRED_IO
+	if (info->fbdefio)
+		fb_deferred_io_open(info, inode, file);
+#endif
 out:
 	unlock_fb_info(info);
 	if (res)
diff --git a/include/linux/fb.h b/include/linux/fb.h
index a8dccd23c249..ecfbcc0553a5 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -659,6 +659,9 @@ 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 void fb_deferred_io_open(struct fb_info *info,
+				struct inode *inode,
+				struct file *file);
 extern void fb_deferred_io_cleanup(struct fb_info *info);
 extern int fb_deferred_io_fsync(struct file *file, loff_t start,
 				loff_t end, int datasync);
-- 
2.30.2


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