s390/mm: implement set_memory_4k()

Implement set_memory_4k() which will split any present large or huge
mapping in the given range to a 4k mapping.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/include/asm/set_memory.h

···
 #define SET_MEMORY_RW	2UL
 #define SET_MEMORY_NX	4UL
 #define SET_MEMORY_X	8UL
+#define SET_MEMORY_4K  16UL
 
 int __set_memory(unsigned long addr, int numpages, unsigned long flags);
 
···
 static inline int set_memory_x(unsigned long addr, int numpages)
 {
 	return __set_memory(addr, numpages, SET_MEMORY_X);
+}
+
+static inline int set_memory_4k(unsigned long addr, int numpages)
+{
+	return __set_memory(addr, numpages, SET_MEMORY_4K);
 }
 
 #endif

arch/s390/mm/pageattr.c

···
 {
 	pte_t *ptep, new;
 
+	if ((flags & SET_MEMORY_4K) == SET_MEMORY_4K)
+		return 0;
 	ptep = pte_offset_kernel(pmdp, addr);
 	do {
 		new = *ptep;
···
 			  unsigned long flags)
 {
 	unsigned long next;
+	int need_split;
 	pmd_t *pmdp;
 	int rc = 0;
 
···
 			return -EINVAL;
 		next = pmd_addr_end(addr, end);
 		if (pmd_large(*pmdp)) {
-			if (addr & ~PMD_MASK || addr + PMD_SIZE > next) {
+			need_split  = !!(flags & SET_MEMORY_4K);
+			need_split |= !!(addr & ~PMD_MASK);
+			need_split |= !!(addr + PMD_SIZE > next);
+			if (need_split) {
 				rc = split_pmd_page(pmdp, addr);
 				if (rc)
 					return rc;
···
 			  unsigned long flags)
 {
 	unsigned long next;
+	int need_split;
 	pud_t *pudp;
 	int rc = 0;
 
···
 			return -EINVAL;
 		next = pud_addr_end(addr, end);
 		if (pud_large(*pudp)) {
-			if (addr & ~PUD_MASK || addr + PUD_SIZE > next) {
+			need_split  = !!(flags & SET_MEMORY_4K);
+			need_split |= !!(addr & ~PUD_MASK);
+			need_split |= !!(addr + PUD_SIZE > next);
+			if (need_split) {
 				rc = split_pud_page(pudp, addr);
 				if (rc)
 					break;