arm64: tlb: fix the TTL value of tlb_get_level

The TTL field indicates the level of page table walk holding the *leaf*
entry for the address being invalidated. But currently, the TTL field
may be set to an incorrent value in the following stack:

pte_free_tlb
    __pte_free_tlb
        tlb_remove_table
            tlb_table_invalidate
                tlb_flush_mmu_tlbonly
                    tlb_flush

In this case, we just want to flush a PTE page, but the tlb->cleared_pmds
is set and we get tlb_level = 2 in the tlb_get_level() function. This may
cause some unexpected problems.

This patch set the TTL field to 0 if tlb->freed_tables is set. The
tlb->freed_tables indicates page table pages are freed, not the leaf
entry.

Cc: <stable@vger.kernel.org> # 5.9.x
Fixes: c4ab2cb ("arm64: tlb: Set the TTL field in flush_tlb_range")
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: ZhuRui <zhurui3@huawei.com>
Signed-off-by: Zhenyu Ye <yezhenyu2@huawei.com>
Link: https://lore.kernel.org/r/b80ead47-1f88-3a00-18e1-cacc22f54cc4@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: Zhenyu Ye

arch/arm64/include/asm/tlb.h

@@ -28,6 +28,10 @@ static void tlb_flush(struct mmu_gather *tlb);
  */
 static inline int tlb_get_level(struct mmu_gather *tlb)
 {
+	/* The TTL field is only valid for the leaf entry. */
+	if (tlb->freed_tables)
+		return 0;
+
 	if (tlb->cleared_ptes && !(tlb->cleared_pmds ||
 				   tlb->cleared_puds ||
 				   tlb->cleared_p4ds))