>
> In a VM, Linux panic information (reason for the panic, stack trace,
> etc.) may be written to a serial console and/or a virtual frame buffer for a
> graphics console. The latter may need to be flushed back to the host
> hypervisor
> for display.
>
> The current Hyper-V DRM driver for the frame buffer does the flushing
> *after* the VMBus connection has been unloaded, such that panic messages are
> not displayed on the graphics console. A user with a Hyper-V graphics console
> is
> left with just a hung empty screen after a panic. The enhanced control that
> DRM
> provides over the panic display in the graphics console is similarly
> non-functional.
>
> Commit 3671f3777758 ("drm/hyperv: Add support for drm_panic") added the
> Hyper-V DRM driver support to flush the virtual frame buffer. It provided
> necessary functionality but did not handle the sequencing problem with VMBus
> unload.
>
> Fix the full problem by using VMBus functions to suppress the VMBus unload
> that
> is normally done by the VMBus driver in the panic path. Then after the frame
> buffer has been flushed, do the VMBus unload so that a kdump kernel can start
> cleanly. As expected, CONFIG_DRM_PANIC must be selected for these changes to
> have effect. As a side benefit, the enhanced features of the DRM panic path
> are
> also functional.
>
> Fixes: 3671f3777758 ("drm/hyperv: Add support for drm_panic")
> Signed-off-by: Michael Kelley <[email protected]>
Reviewed-by: Long Li <[email protected]>
> ---
> drivers/gpu/drm/hyperv/hyperv_drm_drv.c | 4 ++++
> drivers/gpu/drm/hyperv/hyperv_drm_modeset.c | 15 ++++++++-------
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> index 06b5d96e6eaf..79e51643be67 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> @@ -150,6 +150,9 @@ static int hyperv_vmbus_probe(struct hv_device *hdev,
> goto err_free_mmio;
> }
>
> + /* If DRM panic path is stubbed out VMBus code must do the unload */
> + if (IS_ENABLED(CONFIG_DRM_PANIC) &&
> IS_ENABLED(CONFIG_PRINTK))
> + vmbus_set_skip_unload(true);
> drm_client_setup(dev, NULL);
>
> return 0;
> @@ -169,6 +172,7 @@ static void hyperv_vmbus_remove(struct hv_device
> *hdev)
> struct drm_device *dev = hv_get_drvdata(hdev);
> struct hyperv_drm_device *hv = to_hv(dev);
>
> + vmbus_set_skip_unload(false);
> drm_dev_unplug(dev);
> drm_atomic_helper_shutdown(dev);
> vmbus_close(hdev->channel);
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
> b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
> index 7978f8c8108c..d48ca6c23b7c 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
> @@ -212,15 +212,16 @@ static void hyperv_plane_panic_flush(struct
> drm_plane *plane)
> struct hyperv_drm_device *hv = to_hv(plane->dev);
> struct drm_rect rect;
>
> - if (!plane->state || !plane->state->fb)
> - return;
> + if (plane->state && plane->state->fb) {
> + rect.x1 = 0;
> + rect.y1 = 0;
> + rect.x2 = plane->state->fb->width;
> + rect.y2 = plane->state->fb->height;
>
> - rect.x1 = 0;
> - rect.y1 = 0;
> - rect.x2 = plane->state->fb->width;
> - rect.y2 = plane->state->fb->height;
> + hyperv_update_dirt(hv->hdev, &rect);
> + }
>
> - hyperv_update_dirt(hv->hdev, &rect);
> + vmbus_initiate_unload(true);
> }
>
> static const struct drm_plane_helper_funcs hyperv_plane_helper_funcs = {
> --
> 2.25.1
