[PATCH] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

Dexuan Cui
2014-06-26T00:59:21Z

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.
MS-TFS: 157532

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.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