Linux kernel KVM on arm64 miscomputes VNCR stage-1 TLB invalidation size when the S1 MMU is off (S1_MMU_DISABLED=-127), as pgshift_level_to_ttl() mishandles negative levels, resulting in invalidation size 0. A local attacker can trigger stale mappings across contexts, risking guest-to-host isolation bypass with Confidentiality/Integrity/Availability impact. Patch with commits 1c9fca34b962, 8053393680d4, be54a70067c7 or upgrade to a fixed kernel: 6.18.51 , 7.2.5 and 7.3-rc1 to mitigate.