arm64: mask out POIndex when modifying a PTE

When a PTE is modified, the POIndex must be masked off so that it can be modified.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20240822151113.1479789-16-joey.gouly@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/pgtable.h

@@ -1103,7 +1103,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 	 */
 	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
 			      PTE_PRESENT_INVALID | PTE_VALID | PTE_WRITE |
-			      PTE_GP | PTE_ATTRINDX_MASK;
+			      PTE_GP | PTE_ATTRINDX_MASK | PTE_PO_IDX_MASK;
+
 	/* preserve the hardware dirty information */
 	if (pte_hw_dirty(pte))
 		pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));