---
id: CVE-2026-79609
title: |-
  XPTI (Xen Page Table Isolation) was introduced to mitigate Meltdown
  (CVE-2017-5754, one aspect of XSA-254)
summary: |-
  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 a…
severity: none
published: '2026-10-13'
updated: '2026-10-13'
sourceUpdated: '2026-10-13T17:17:46.773'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-79609'
references:
  - url: 'https://xenbits.xenproject.org/xsa/advisory-516.html'
    label: security@xen.org
  - url: 'http://xenbits.xen.org/xsa/advisory-516.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
ingestedAt: '2026-10-13T16:35:46.745Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.