[PATCH] drm/hyperv: Fix device removal on Gen1 VMs

[Mohammed Gamal]

The Hyper-V DRM driver tries to free MMIO region on removing
the device regardless of VM type, while Gen1 VMs don't use MMIO
and hence causing the kernel to crash on a NULL pointer dereference.

Fix this by making deallocating MMIO only on Gen2 machines and implement
removal for Gen1

Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video 
device")

Signed-off-by: Mohammed Gamal <mga...@redhat.com>
---
 drivers/gpu/drm/hyperv/hyperv_drm_drv.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c 
b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
index cd818a629183..9f923beb7d8d 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
@@ -225,12 +225,29 @@ static int hyperv_vmbus_remove(struct hv_device *hdev)
 {
        struct drm_device *dev = hv_get_drvdata(hdev);
        struct hyperv_drm_device *hv = to_hv(dev);
+       struct pci_dev *pdev;
 
        drm_dev_unplug(dev);
        drm_atomic_helper_shutdown(dev);
        vmbus_close(hdev->channel);
        hv_set_drvdata(hdev, NULL);
-       vmbus_free_mmio(hv->mem->start, hv->fb_size);
+
+       /*
+        * Free allocated MMIO memory only on Gen2 VMs.
+        * On Gen1 VMs, release the PCI device
+        */
+       if (efi_enabled(EFI_BOOT)) {
+               vmbus_free_mmio(hv->mem->start, hv->fb_size);
+       } else {
+               pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT,
+                               PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
+               if (!pdev) {
+                       drm_err(dev, "Unable to find PCI Hyper-V video\n");
+                       return -ENODEV;
+               }
+               pci_release_region(pdev, 0);
+               pci_dev_put(pdev);
+       }
 
        return 0;
 }
-- 
2.33.1