hyperv_fb: Update screen_info after removing old framebuffer

On gen2 HyperV VM, hyperv_fb will remove the old framebuffer, and the
new allocated framebuffer address could be at a differnt location,
and it might be no longer a VGA framebuffer.

Update screen_info so that after kexec the kernel won't try to reuse
the old invalid/stale framebuffer address as VGA, corrupting memory.

[ mingo: Tidied up the changelog. ]

Signed-off-by: Kairui Song <kasong@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Jake Oshins <jakeo@microsoft.com>
Cc: Wei Hu <weh@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Link: https://lore.kernel.org/r/20201014092429.1415040-3-kasong@redhat.com

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index 02411d89cb462e2f98b0960f480f3fafb7abae91..e36fb1a0ecdbdb40dae4c3339a9c0bcaf2e65ada 100644 (file)
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -1114,8 +1114,15 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 getmem_done:
        remove_conflicting_framebuffers(info->apertures,
                                        KBUILD_MODNAME, false);
-       if (!gen2vm)
+
+       if (gen2vm) {
+               /* framebuffer is reallocated, clear screen_info to avoid misuse from kexec */
+               screen_info.lfb_size = 0;
+               screen_info.lfb_base = 0;
+               screen_info.orig_video_isVGA = 0;
+       } else {
                pci_dev_put(pdev);
+       }
        kfree(info->apertures);
 
        return 0;