# CVE-2026-97526: s390/pai: Support CPU hotplug for PMU PAI

CVE-2026-97526 is fixed in linux on 1 platform by DEBIAN-CVE-2026-97526 (version 7.2.7-1), released October 2, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-97526
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 25, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-97526

## Description

In the Linux kernel, the following vulnerability has been resolved:  s390/pai: Support CPU hotplug for PMU PAI  The command 'perf stat -e pai_crypto/CRYPTO_ALL/ -- <command>' crashes the kernel when CPUs are hotplug added during that run.  Root cause is the missing allocation of per-CPU data structures for that new CPU. The allocation is dynamic and the first event that has task context creates such a structure for each online CPU. This is not sufficient. CPUs may be offline during event creation and can be set online during the perf run time. For example commands   # echo 0 > /sys/devices/system/cpu/cpu1/online  # perf stat -e cycles -i -- stress-ng -t10s --matrix X  # sleep 1  # echo 1 > /sys/devices/system/cpu/cpu1/online  Currently without a CPU hotplug handler, that new CPU has no per-CPU data infrastructure. The scheduler runs PMU call back function pai_add() to install the PMU support for that CPU before the task is being scheduled on that new CPU. In pai_add() instructions      mp = this_cpu_ptr(pai_root[idx].mapptr);     cpump = mp->mapptr;  return a NULL pointer and the result is a kernel panic as variable cpump is used inside that function.  Add CPU hotplug support for CPU add and delete and create the necessary per-CPU data infrastructure during CPU hotplug add processing. Same for CPU hotplug remove. This is done when the CPU is offline to ensure the data structures are available when CPU is made online and tasks are scheduled on it.  [hca@linux.ibm.com: fixup error path in pai_init()]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.7-1 | [DEBIAN-CVE-2026-97526](https://patchblox.com/security/data/fix/linux/debian-cve-2026-97526.md) | Oct 2, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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