Grub changed?

kristi · July 2, 2025, 3:51pm

I noticed that my grub after a recent update has this:
. /etc/default/grub.qubes-kernel-vm-support
can someone please explain what is that and why is it appeared all of the sudden?
I also noticed some other changes within it, but I guess it’s all related.

Also, how can I preserve my smt=on setting, so it won’t change back to smt=off please?

alimirjamali · July 2, 2025, 4:07pm

That file existing since 2019. Here is its source:

github.com/QubesOS/qubes-linux-utils

grub/grub.qubes-kernel-vm-support

main

# add kernel options only in VM, and only if initramfs is updated already
# /var/lib/qubes/initramfs-updated contains "milestone" initramfs update version:
# 1 - addition of xen scrub_pages enabling code
if [ -r /usr/share/qubes/marker-vm ] &&
        [ "$(cat /var/lib/qubes/initramfs-updated 2>/dev/null || echo 0)" -ge 1 ]; then
    GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX xen_scrub_pages=0"
fi
GRUB_ENABLE_BLSCFG=false
# Add qubes version to boot menu on dom0
if [ -f "/etc/qubes-release" ]; then
    GRUB_DISTRIBUTOR="$(sed 's,\(.*\) release \(.*\) (R\(.*\)),\1 (R\3),g' /etc/system-release)"
fi

If you take a look into commit history (and notes), it should provide some background on why it is necessary and what it does.

Take a look at /etc/default/grub in dom0. And look for GRUB_CMDLINE_XEN_DEFAULT

kristi · July 2, 2025, 4:17pm

I just don’t really recall that line from before, I’m pretty sure it wasn’t there before the update.

Also, I had smt=on before the update within the GRUB_XMDLINE_XEN_DEFAULT, but after the update it added at the bottom new GRUB_XMDLINE_XEN_DEFAULT with smt=off

renehoj · July 2, 2025, 4:44pm

You need to add the smt=on line after smt=off.

The update script checks if the file contains smt=off, if it’s missing it will be added to grub.

kristi · July 2, 2025, 4:49pm

Thank you!