s390/vmem: do not silently ignore mapping limit

The only interface that allows drivers establishing
liner mappings is vmem_add_mapping(). It does check
a requested range against allowed limits and a call
to modify_pagetable() with an invalid mapping range
is impossible.

Hence, an attempt to map an address range outside of
the identity mapping or vmemmap array could only be
kernel bug.
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/mm/vmem.c

@@ -290,14 +290,9 @@ static int __ref modify_pmd_table(pud_t *pud, unsigned long addr,
 
 static void try_free_pmd_table(pud_t *pud, unsigned long start)
 {
-	const unsigned long end = start + PUD_SIZE;
 	pmd_t *pmd;
 	int i;
 
-	/* Don't mess with any tables not fully in 1:1 mapping & vmemmap area */
-	if (end > VMALLOC_START)
-		return;
-
 	pmd = pmd_offset(pud, start);
 	for (i = 0; i < PTRS_PER_PMD; i++, pmd++)
 		if (!pmd_none(*pmd))
@@ -362,14 +357,9 @@ static int modify_pud_table(p4d_t *p4d, unsigned long addr, unsigned long end,
 
 static void try_free_pud_table(p4d_t *p4d, unsigned long start)
 {
-	const unsigned long end = start + P4D_SIZE;
 	pud_t *pud;
 	int i;
 
-	/* Don't mess with any tables not fully in 1:1 mapping & vmemmap area */
-	if (end > VMALLOC_START)
-		return;
-
 	pud = pud_offset(p4d, start);
 	for (i = 0; i < PTRS_PER_PUD; i++, pud++) {
 		if (!pud_none(*pud))
@@ -412,14 +402,9 @@ static int modify_p4d_table(pgd_t *pgd, unsigned long addr, unsigned long end,
 
 static void try_free_p4d_table(pgd_t *pgd, unsigned long start)
 {
-	const unsigned long end = start + PGDIR_SIZE;
 	p4d_t *p4d;
 	int i;
 
-	/* Don't mess with any tables not fully in 1:1 mapping & vmemmap area */
-	if (end > VMALLOC_START)
-		return;
-
 	p4d = p4d_offset(pgd, start);
 	for (i = 0; i < PTRS_PER_P4D; i++, p4d++) {
 		if (!p4d_none(*p4d))
@@ -439,6 +424,9 @@ static int modify_pagetable(unsigned long start, unsigned long end, bool add,
 
 	if (WARN_ON_ONCE(!PAGE_ALIGNED(start | end)))
 		return -EINVAL;
+	/* Don't mess with any tables not fully in 1:1 mapping & vmemmap area */
+	if (WARN_ON_ONCE(end > VMALLOC_START))
+		return -EINVAL;
 	for (addr = start; addr < end; addr = next) {
 		next = pgd_addr_end(addr, end);
 		pgd = pgd_offset_k(addr);