Drivers: hv: vmbus: Provide option to skip VMBus unload on panic

Currently, VMBus code initiates a VMBus unload in the panic path so
that if a kdump kernel is loaded, it can start fresh in setting up its
own VMBus connection. However, a driver for the VMBus virtual frame
buffer may need to flush dirty portions of the frame buffer back to
the Hyper-V host so that panic information is visible in the graphics
console. To support such flushing, provide exported functions for the
frame buffer driver to specify that the VMBus unload should not be
done by the VMBus driver, and to initiate the VMBus unload itself.
Together these allow a frame buffer driver to delay the VMBus unload
until after it has completed the flush.

Ideally, the VMBus driver could use its own panic-path callback to do
the unload after all frame buffer drivers have finished. But DRM frame
buffer drivers use the kmsg dump callback, and there are no callbacks
after that in the panic path. Hence this somewhat messy approach to
properly sequencing the frame buffer flush and the VMBus unload.

Fixes: 3671f3777758 ("drm/hyperv: Add support for drm_panic")
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 964f1be8150c..41a3d82f0722 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1336,6 +1336,9 @@ int vmbus_allocate_mmio(struct resource **new, struct hv_device *device_obj,
 			bool fb_overlap_ok);
 void vmbus_free_mmio(resource_size_t start, resource_size_t size);
 
+void vmbus_initiate_unload(bool crash);
+void vmbus_set_skip_unload(bool skip);
+
 /*
  * GUID definitions of various offer types - services offered to the guest.
  */