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[bug #56217] Grub2 Booting in blind mode due to "invalid video mode spec

From: Dexuan Cui
Subject: [bug #56217] Grub2 Booting in blind mode due to "invalid video mode specification `text'"
Date: Thu, 25 Apr 2019 16:17:18 -0400 (EDT)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36


                 Summary: Grub2 Booting in blind mode due to "invalid video
mode specification `text'"
                 Project: GNU GRUB
            Submitted by: decui
            Submitted on: Thu 25 Apr 2019 08:17:16 PM UTC
                Category: Booting
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: Git master
         Reproducibility: Every Time
         Planned Release: None



In a Ubuntu 16.04.6 VM, which runs as a Gen2 VM on Hyper-V, I add
GRUB_GFXPAYLOAD_LINUX="text" into /etc/default/grub and run update-grub; next,
grub2 prints the below error:
error: invalid video mode specification `text'.
Booting in blind mode

This means grub2 passes a zero value for the "lfb_base" to
Linux kernel, which then fails to reserve the framebuffer MMIO range in
drivers/hv/vmbus_drv.c: vmbus_reserve_fb(); as a result, when we pass through
a PCIe device to the VM, the PCIe device may get a PCI MMIO BAR in the FB MMIO
range, causing a conflict, and the PCIe device can not work in the VM.

The issue can not reproduce with Ubuntu 18.04. It turns out the grub2 in
Ubuntu 18.04 has the below fix:

video: skip 'text' gfxpayload if not supported, to fallback to default

I'm asking the patch author (Mathieu Trudel-Lapierre) to submit the patch to
the upstream grub, and hence I'm reporting this bug to track the issue. :-) 
Once the fix is in the upstream grub, it would easier to ask the other Linux
distros, e.g. RHEL 7.6, to also integrate the fix.


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