qubes-linux-utils/grub/grub.qubes-kernel-vm-support

# add kernel options only in VM
if [ -r /usr/share/qubes/marker-vm ]; then
    GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX xen_scrub_pages=0"
fi
Disable scrubbing memory pages during initial balloon down Balloon driver scrub memory page before giving it back to the hypervisor. Normally this is a good thing, to avoid leaking VM's memory data into Xen and other domains. But during initial startup when maxmem is bigger than initial memory, on HVM and PVH, Populate-on-Demand (PoD) is in use. This means every page on initial balloon down needs to be first mapped by Xen into VM's memory (as it wasn't populated before - and in fact didn't have any data), scrubbed by the kernel and then given back to Xen. This is great waste of time. Such operation with default settings (initial memory 400M, maxmem 4000M) can take few seconds, delaying every VM startup (including DispVM). In extreme situation, when running inside nested virtualization, the effect is much worse. Avoid this problem by disabling memory scrubbing during initial boot, and re-enable it as soon as user space kicks in - in initramfs, before mounting root filesystem, to be sure it's enabled before memory contains any kind of secrets. This commit handle only one case - when kernel in managed by the VM itself. It is critical to enable initramfs module whenever xen_scrub_pages=0 kernel option is given, so make them depend on the same condition and ship them in the same package. Fixes QubesOS/qubes-issues#1963 2019-01-18 22:53:20 +00:00			`# add kernel options only in VM`
			`if [ -r /usr/share/qubes/marker-vm ]; then`
			`GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX xen_scrub_pages=0"`
			`fi`