linux-kernel - [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

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Date:	Thu, 26 Jun 2014 14:35:01 -0700
From:	Dexuan Cui <decui@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, plagnioj@...osoft.com,
	tomi.valkeinen@...com, linux-fbdev@...r.kernel.org, olaf@...fle.de,
	apw@...onical.com, jasowang@...hat.com
Cc:	kys@...rosoft.com, haiyangz@...rosoft.com
Subject: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

Currently the VSC has no chance to notify the VSP of the dirty rectangle on VM
panic because the notification work is done in a workqueue, and in panic() the
kernel typically ends up in an infinite loop, and a typical kernel config has
CONFIG_PREEMPT_VOLUNTARY=y and CONFIG_PREEMPT is not set, so a context switch
can't happen in panic() and the workqueue won't have a chance to run. As a
result, the VM Connection window can't refresh until it's closed and we
re-connect to the VM.

We can register a handler on panic_notifier_list: the handler can notify
the VSC and switch the framebuffer driver to a "synchronous mode", meaning
the VSC flushes any future framebuffer change to the VSP immediately.

v2: removed the MS-TFS line in the commit message

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
---
 drivers/video/fbdev/hyperv_fb.c | 58 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index e23392e..291d171 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -226,11 +226,16 @@ struct hvfb_par {
 	u8 recv_buf[MAX_VMBUS_PKT_SIZE];
 };
 
+static struct fb_info *hvfb_info;
+
 static uint screen_width = HVFB_WIDTH;
 static uint screen_height = HVFB_HEIGHT;
 static uint screen_depth;
 static uint screen_fb_size;
 
+/* If true, the VSC notifies the VSP on every framebuffer change */
+static bool synchronous_fb;
+
 /* Send message to Hyper-V host */
 static inline int synthvid_send(struct hv_device *hdev,
 				struct synthvid_msg *msg)
@@ -532,6 +537,20 @@ static void hvfb_update_work(struct work_struct *w)
 		schedule_delayed_work(&par->dwork, HVFB_UPDATE_DELAY);
 }
 
+static int hvfb_on_panic(struct notifier_block *nb,
+			unsigned long e, void *p)
+{
+	if (hvfb_info)
+		synthvid_update(hvfb_info);
+
+	synchronous_fb = true;
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block hvfb_panic_nb = {
+	.notifier_call = hvfb_on_panic,
+};
 
 /* Framebuffer operation handlers */
 
@@ -582,14 +601,41 @@ static int hvfb_blank(int blank, struct fb_info *info)
 	return 1;	/* get fb_blank to set the colormap to all black */
 }
 
+static void hvfb_cfb_fillrect(struct fb_info *p,
+				const struct fb_fillrect *rect)
+{
+	cfb_fillrect(p, rect);
+
+	if (unlikely(synchronous_fb))
+		synthvid_update(p);
+}
+
+static void hvfb_cfb_copyarea(struct fb_info *p,
+				const struct fb_copyarea *area)
+{
+	cfb_copyarea(p, area);
+
+	if (unlikely(synchronous_fb))
+		synthvid_update(p);
+}
+
+static void hvfb_cfb_imageblit(struct fb_info *p,
+				const struct fb_image *image)
+{
+	cfb_imageblit(p, image);
+
+	if (unlikely(synchronous_fb))
+		synthvid_update(p);
+}
+
 static struct fb_ops hvfb_ops = {
 	.owner = THIS_MODULE,
 	.fb_check_var = hvfb_check_var,
 	.fb_set_par = hvfb_set_par,
 	.fb_setcolreg = hvfb_setcolreg,
-	.fb_fillrect = cfb_fillrect,
-	.fb_copyarea = cfb_copyarea,
-	.fb_imageblit = cfb_imageblit,
+	.fb_fillrect = hvfb_cfb_fillrect,
+	.fb_copyarea = hvfb_cfb_copyarea,
+	.fb_imageblit = hvfb_cfb_imageblit,
 	.fb_blank = hvfb_blank,
 };
 
@@ -801,6 +847,9 @@ static int hvfb_probe(struct hv_device *hdev,
 
 	par->fb_ready = true;
 
+	hvfb_info = info;
+	atomic_notifier_chain_register(&panic_notifier_list, &hvfb_panic_nb);
+
 	return 0;
 
 error:
@@ -820,6 +869,9 @@ static int hvfb_remove(struct hv_device *hdev)
 	struct fb_info *info = hv_get_drvdata(hdev);
 	struct hvfb_par *par = info->par;
 
+	atomic_notifier_chain_unregister(&panic_notifier_list, &hvfb_panic_nb);
+	hvfb_info = NULL;
+
 	par->update = false;
 	par->fb_ready = false;
 
-- 
1.9.1

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