---
id: CVE-2026-89593
title: 'hugetlb: only adjust reservation during unmapping if mapcount is 0'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  hugetlb: only adjust reservation during unmapping if mapcount is 0

  Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations.  In
  the case of folio mapped in …
severity: high
cvss: 7.1
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-191
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 <
    b0b1b9ca80b795ed2223e76dd787db7067121fb9
  - >-
    Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 <
    a3c65af20cceb7f997847727636b4017326f845d
  - >-
    Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 <
    0f001491e5a2ec69aa9d5dd6b799e5742245f9ea
  - >-
    Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 <
    5120b1e048d48596ffaec1a8412012a91adba73b
  - Linux 6.9
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:49:25.740Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89593'
references:
  - url: 'https://git.kernel.org/stable/c/b0b1b9ca80b795ed2223e76dd787db7067121fb9'
  - url: 'https://git.kernel.org/stable/c/a3c65af20cceb7f997847727636b4017326f845d'
  - url: 'https://git.kernel.org/stable/c/0f001491e5a2ec69aa9d5dd6b799e5742245f9ea'
  - url: 'https://git.kernel.org/stable/c/5120b1e048d48596ffaec1a8412012a91adba73b'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89593.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89593'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532027'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89593'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89593'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89593.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00125
epssPercentile: 0.02225
scores:
  cna: 7.1
  vendor: 5.5
ingestedAt: '2026-09-14T15:23:07.451Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

hugetlb: only adjust reservation during unmapping if mapcount is 0

Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations.  In
the case of folio mapped in both a parent and a child, if the parent
unmaps the range first, the reservation adjustment will result in an
underflow of the reserved count.  Once the child unmaps the range, the
count is restored.  Change __unmap_hugepage_range() to check the mapcount
before adjusting the reservation.

## Affected

- `Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 < b0b1b9ca80b795ed2223e76dd787db7067121fb9`
- `Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 < a3c65af20cceb7f997847727636b4017326f845d`
- `Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 < 0f001491e5a2ec69aa9d5dd6b799e5742245f9ea`
- `Linux >= df7a6d1f64056aec572162c5d35ed9ff86ece6f3 < 5120b1e048d48596ffaec1a8412012a91adba73b`
- `Linux 6.9`

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-10-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89593.json)