Linux Kernel EUVD-2026-27817

This vulnerability affects the Linux kernel's memory management subsystem specifically on the Alpha CPU architecture. The root cause is a failure in Translation Lookaside Buffer (TLB) synchronization during page migration and memory compaction operations. Alpha processors use Address Space Number (ASN) based memory management context switching for instruction cache coherency, but this mechanism alone cannot guarantee that stale TLB entries are properly invalidated when pages are migrated during compaction. The vulnerability arises because Alpha's MM context rollover does not include adequate cross-CPU TLB shootdown operations, allowing outdated virtual-to-physical address translations to persist after page migration. This creates a race condition where user-space processes may reference stale physical addresses, resulting in heap corruption and segmentation faults. The fix introduces a migration-specific helper combining ASN rollover, immediate per-CPU TLB invalidation via TBI instruction, and synchronous cross-CPU TLB shootdown, while also adding proper memory ordering primitives (READ_ONCE/WRITE_ONCE) to flush_tlb_other() and pte_clear() functions to prevent compiler reordering issues in SMP environments.