arm64: Restrict pagetable teardown to avoid false warning

Commit 9c00697 ("arm64: mmu: drop pXd_present() checks from
pXd_free_pYd_table()") removes the pxd_present() checks because the
caller checks pxd_present(). But, in case of vmap_try_huge_pud(), the
caller only checks pud_present(); pud_free_pmd_page() recurses on each
pmd through pmd_free_pte_page(), wherein the pmd may be none. Thus it is
possible to hit a warning in the latter, since pmd_none => !pmd_table().
Thus, add a pmd_present() check in pud_free_pmd_page().

This problem was found by code inspection.

Fixes: 9c00697 ("arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table()")
Cc: [email protected]
Reported-by: Ryan Roberts <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Signed-off-by: Dev Jain <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Reviewed-by: Ryan Roberts <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Dev Jain

arch/arm64/mm/mmu.c

@@ -1305,7 +1305,8 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 	next = addr;
 	end = addr + PUD_SIZE;
 	do {
-		pmd_free_pte_page(pmdp, next);
+		if (pmd_present(pmdp_get(pmdp)))
+			pmd_free_pte_page(pmdp, next);
 	} while (pmdp++, next += PMD_SIZE, next != end);
 
 	pud_clear(pudp);