CVE-2025-39961: 
Linux Kernel vulnerability analysis and mitigation

A race condition vulnerability was identified in the Linux kernel's AMD IOMMU host page table implementation (CVE-2025-39961). The vulnerability was disclosed on October 9, 2025, affecting the page table level management in the AMD IOMMU driver (NVD).

The vulnerability exists in the AMD IOMMU host page table implementation which supports dynamic page table levels (up to 6 levels), starting with a 3-level configuration. The issue occurs in the unmap path (iommuv1unmappages()) where fetchpte() reads pgtable->[root/mode] without proper locking. When increaseaddressspace() is updating pgtable->[root/mode], fetch_pte() may read an incorrect page table level, resulting in operation failures. The vulnerability has been assigned a CVSS v3.1 score of 7.0, indicating moderate severity (Red Hat).

When exploited, this vulnerability can cause iommuunmap operations to fail, potentially leading to system instability. The upper layer may retry operations or log WARNON messages, affecting system reliability (NVD).

The fix implements seqcount to enable lock-free read operations on the read path, as page table level updates are infrequent and already synchronized with a spinlock. This solution has been incorporated into the Linux kernel (NVD).