arm64: mm: Correct show_pte behaviour

show_pte makes use of the *_none_or_clear_bad style functions. If a
pgd, pud or pmd is identified as being bad, it will then be cleared.

As show_pte appears to be called from either the user or kernel
fault handlers this side effect can lead to unpredictable behaviour;
especially as TLB entries are not invalidated.

This patch removes the page table sanitisation from show_pte. If a
bad pgd, pud or pmd is encountered it is left unmodified.

Signed-off-by: Steve Capper <steve.capper@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/fault.c

@@ -57,16 +57,16 @@ void show_pte(struct mm_struct *mm, unsigned long addr)
 		pmd_t *pmd;
 		pte_t *pte;
 
-		if (pgd_none_or_clear_bad(pgd))
+		if (pgd_none(*pgd) || pgd_bad(*pgd))
 			break;
 
 		pud = pud_offset(pgd, addr);
-		if (pud_none_or_clear_bad(pud))
+		if (pud_none(*pud) || pud_bad(*pud))
 			break;
 
 		pmd = pmd_offset(pud, addr);
 		printk(", *pmd=%016llx", pmd_val(*pmd));
-		if (pmd_none_or_clear_bad(pmd))
+		if (pmd_none(*pmd) || pmd_bad(*pmd))
 			break;
 
 		pte = pte_offset_map(pmd, addr);