From: "George Dunlap" <dunlapg@umich.edu>
To: "Francis Greaves" <francis@choughs.net>, "centos-virt" <centos-virt@centos.org>
Sent: Tuesday, 23 February, 2016 09:31:40
Subject: Re: [CentOS-virt] Garbled screen after RAM Scrub on boot

On Mon, Feb 22, 2016 at 4:18 PM, Francis Greaves <francis@choughs.net> wrote:
> Dear All
> I am using Centos 7 with Xen 4.6 on a Dell Poweredge T430
> When the machine boots, after the 'Scrubbing Free RAM' message, I get a
> screen filled with little white squares until the login prompt, so I cannot
> see what is happening as the machine boots. Also there is nothing on the
> screen when I reboot.
>
> My /etc/default/grub is
>
> GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
> GRUB_DEFAULT=saved
> GRUB_DISABLE_SUBMENU=true
> GRUB_CMDLINE_LINUX="crashkernel=auto rhgb intremap=no_x2apic_optout"
> GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=13312M,max:14336M dom0_max_vcpus=6
> dom0_vcpus_pin"
> GRUB_GFXMODE=1024x768
> GRUB_GFXPAYLOAD_LINUX=keep
> GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT="console=hvc0 earlyprintk=xen
> nomodeset"
>
> I have tried setting (for a 1024x768 resolution) vga=792 in the
> GRUB_CMDLINE_LINUX and commenting out GRUB_GFXMODE and
> GRUB_GFXPAYLOAD_LINUX, but this makes no difference
>
> What am I doing wrong?

Francis,

Thanks for reporting this.  I'd suggest re-posting your question on
xen-users -- there are a lot more eyeballs watching that list than
this one, and it's easier to "escalate" the issue to the development
list from there.

My first instinct is wondering whether grub setting the graphics mode
is part of the problem.  Have you tried having grub just take the bios
text mode that was given it, rather than changing it?

(Obviously ideally Xen would work whatever the graphics mode is, but
most developers are accessing test boxes over serial in a colo, so
it's not the kind of thing they're prone to notice.)

 -George