• Marek Marczykowski-Górecki's avatar
    xen/balloon: add runtime control for scrubbing ballooned out pages · 197ecb38
    Marek Marczykowski-Górecki authored
    Scrubbing pages on initial balloon down can take some time, especially
    in nested virtualization case (nested EPT is slow). When HVM/PVH guest is
    started with memory= significantly lower than maxmem=, all the extra
    pages will be scrubbed before returning to Xen. But since most of them
    weren't used at all at that point, Xen needs to populate them first
    (from populate-on-demand pool). In nested virt case (Xen inside KVM)
    this slows down the guest boot by 15-30s with just 1.5GB needed to be
    returned to Xen.
    
    Add runtime parameter to enable/disable it, to allow initially disabling
    scrubbing, then enable it back during boot (for example in initramfs).
    Such usage relies on assumption that a) most pages ballooned out during
    initial boot weren't used at all, and b) even if they were, very few
    secrets are in the guest at that time (before any serious userspace
    kicks in).
    Convert CONFIG_XEN_SCRUB_PAGES to CONFIG_XEN_SCRUB_PAGES_DEFAULT (also
    enabled by default), controlling default value for the new runtime
    switch.
    Signed-off-by: Marek Marczykowski-Górecki's avatarMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
    Reviewed-by: Juergen Gross's avatarJuergen Gross <jgross@suse.com>
    Signed-off-by: 's avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    197ecb38
mem-reservation.c 3.2 KB