The Linux kernel vulnerability CVE-2026-72412 affects the s390 architecture's memory management by incorrect handling of the _PAGE_UNUSED softbit in page table entries. This bit signals that a page can be discarded rather than moved or swapped. KVM sets this bit on userspace ptes for unused guest pages but cannot clear it when pages become used again. Previously, only set_ptes() cleared this bit, but other code paths that set new ptes did not, causing used pages to be mistakenly discarded and resulting in guest corruption. The patch clears the _PAGE_UNUSED bit for present ptes in set_pte(), eliminating the issue and removing redundant checks. Additionally, gmap_helper_try_set_pte_unused() was fixed to set the bit only for present ptes, aligning with its definition.

The vulnerability could cause guest memory corruption in virtualized environments using KVM on s390 architecture due to used pages being discarded as unused. This could affect system stability and data integrity within affected guests. There is no indication of remote code execution or privilege escalation from the provided data.

A fix has been implemented in the Linux kernel to clear the _PAGE_UNUSED bit whenever a present pte is set, preventing the erroneous discarding of used pages. Users should apply the official kernel update that includes this patch. Since this is a kernel-level fix, upgrading to the patched kernel version is the recommended mitigation. Patch status is not explicitly stated in the input; check the vendor advisory or Linux kernel mailing lists for the exact fixed version and update accordingly.