Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

XPTI (Xen Page Table Isolation) was introduced to mitigate Meltdown
(CVE-2017-5754, one aspect of XSA-254).  This involves copying 64-bit PV
guest page table entries from guest-chosen root page tables to the Xen-
chosen one which is in actual use by hardware.  To read the guest root
page table, the directmap is used.  PV guests, however, have a directmap
which may not cover all memory; in particular this is the case if any
memory extends beyond the 5 TiB (CONFIG_BIGMEM=y: 3.5 TiB) address
boundary.