CVE-2026-79603

x86 PV guests can free memory pages while still keeping a stale TLB entry
pointing to them.  A TLB flush is only issued by Xen (if needed) when the
page is re-used.  Since it's possible for the page to be scrubbed ahead of
the TLB flush, there's a window where a PV guest can modify an already
scrubbed page.