arm64: fix erroneous warnings in page freeing functions

In pmd_free_pte_page() and pud_free_pmd_page() we try to warn if they
hit a present non-table entry. In both cases we'll warn for non-present
entries, as the VM_WARN_ON() only checks the entry is not a table entry.

This has been observed to result in warnings when booting a v4.19-rc2
kernel under qemu.

Fix this by bailing out earlier for non-present entries.

Fixes: ec28bb9c ("arm64: Implement page table free interfaces")
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/mm/mmu.c

@@ -985,8 +985,9 @@ int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
 
 	pmd = READ_ONCE(*pmdp);
 
-	/* No-op for empty entry and WARN_ON for valid entry */
-	if (!pmd_present(pmd) || !pmd_table(pmd)) {
+	if (!pmd_present(pmd))
+		return 1;
+	if (!pmd_table(pmd)) {
 		VM_WARN_ON(!pmd_table(pmd));
 		return 1;
 	}
@@ -1007,8 +1008,9 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 
 	pud = READ_ONCE(*pudp);
 
-	/* No-op for empty entry and WARN_ON for valid entry */
-	if (!pud_present(pud) || !pud_table(pud)) {
+	if (!pud_present(pud))
+		return 1;
+	if (!pud_table(pud)) {
 		VM_WARN_ON(!pud_table(pud));
 		return 1;
 	}