[tip: x86/urgent] hyperv_fb: Update screen_info after removing old framebuffer

[tip-bot2 for Kairui Song]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     3cb73bc3fa2a3cb80b88aa63b48409939e0d996b
Gitweb:        https://git.kernel.org/tip/3cb73bc3fa2a3cb80b88aa63b48409939e0d996b
Author:        Kairui Song <kasong@xxxxxxxxxx>
AuthorDate:    Wed, 14 Oct 2020 17:24:29 +08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 14 Oct 2020 17:05:26 +02:00

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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Jake Oshins <jakeo@xxxxxxxxxxxxx>
Cc: Wei Hu <weh@xxxxxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201014092429.1415040-3-kasong@xxxxxxxxxx
---
 drivers/video/fbdev/hyperv_fb.c |  9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index 02411d8..e36fb1a 100644
--- 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;