• Roger Pau Monne's avatar
    xen: add helpers to allocate unpopulated memory · 9e2369c0
    Roger Pau Monne authored
    To be used in order to create foreign mappings. This is based on the
    ZONE_DEVICE facility which is used by persistent memory devices in
    order to create struct pages and kernel virtual mappings for the IOMEM
    areas of such devices. Note that on kernels without support for
    ZONE_DEVICE Xen will fallback to use ballooned pages in order to
    create foreign mappings.
    
    The newly added helpers use the same parameters as the existing
    {alloc/free}_xenballooned_pages functions, which allows for in-place
    replacement of the callers. Once a memory region has been added to be
    used as scratch mapping space it will no longer be released, and pages
    returned are kept in a linked list. This allows to have a buffer of
    pages and prevents resorting to frequent additions and removals of
    regions.
    
    If enabled (because ZONE_DEVICE is supported) the usage of the new
    functionality untangles Xen balloon and RAM hotplug from the usage of
    unpopulated physical memory ranges to map foreign pages, which is the
    correct thing to do in order to avoid mappings of foreign pages depend
    on memory hotplug.
    
    Note the driver is currently not enabled on Arm platforms because it
    would interfere with the identity mapping required on some platforms.
    Signed-off-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
    Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
    Link: https://lore.kernel.org/r/20200901083326.21264-4-roger.pau@citrix.comSigned-off-by: default avatarJuergen Gross <jgross@suse.com>
    9e2369c0
xen.h 1.63 KB