In the Linux kernel, the following vulnerability has been resolved:
arm64: tlb: Flush walk cache when unsharing PMD tables
When huge_pmd_unshare() is called to unshare a PMD table, the tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true but the aarch64 tlb_flush() only checked tlb->freed_tables to determine whether to use TLBF_NONE (vae1is, invalidates walk cache) or TLBF_NOWALKCACHE (vale1is, leaf-only).
This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks.
Fix by including unshared_tables in the check, so that when unsharing tables, TLBF_NONE is used and the walk cache is properly invalidated.
Here is the detailed distinction between vae1is and vale1is:
| Instruction Combination | Actual Invalidation Scope |
| ------------------------ | --------------------------------------------------|
| VAE1IS + TTL=0 | All entries at all levels (full invalidation) |
| VAE1IS + TTL=2 (L2) | Non-leaf at Level 0/1 + leaf at Level 2 |
| VALE1IS + TTL=0 | Leaf entries at all levels (non-leaf not cleared) |
| VALE1IS + TTL=2 (L2) | Leaf entry at Level 2 only |