s390/mm: make hugepages_supported a boot time decision

There is a potential bug with KVM and hugetlbfs if the hardware does not
support hugepages (EDAT1). We fix this by making EDAT1 a hard requirement
for hugepages and therefore removing and simplifying code.

As s390, with the sw-emulated hugepages, was the only user of
arch_prepare/release_hugepage I also removed theses calls from common and
other architecture code.

This patch (of 5):

By dropping support for hugepages on machines which do not have the
hardware feature EDAT1, we fix a potential s390 KVM bug.

The bug would happen if a guest is backed by hugetlbfs (not supported
currently), but does not get pagetables with PGSTE. This would lead to
random memory overwrites.

Signed-off-by: Dominik Dingel <[e-mail]>
Acked-by: Martin Schwidefsky <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/s390/include/asm/page.h

···
 #define PAGE_DEFAULT_ACC	0
 #define PAGE_DEFAULT_KEY	(PAGE_DEFAULT_ACC << 4)
 
-#define HPAGE_SHIFT	20
+#include <asm/setup.h>
+#ifndef __ASSEMBLY__
+
+extern unsigned int HPAGE_SHIFT;
 #define HPAGE_SIZE	(1UL << HPAGE_SHIFT)
 #define HPAGE_MASK	(~(HPAGE_SIZE - 1))
 #define HUGETLB_PAGE_ORDER	(HPAGE_SHIFT - PAGE_SHIFT)
···
 #define ARCH_HAS_HUGE_PTE_TYPE
 #define ARCH_HAS_PREPARE_HUGEPAGE
 #define ARCH_HAS_HUGEPAGE_CLEAR_FLUSH
-
-#include <asm/setup.h>
-#ifndef __ASSEMBLY__
 
 static inline void storage_key_init_range(unsigned long start, unsigned long end)
 {

arch/s390/kernel/setup.c

···
 	 */
 	setup_hwcaps();
 
+	HPAGE_SHIFT = MACHINE_HAS_HPAGE ? 20 : 0;
+
 	/*
 	 * Create kernel page tables and switch to virtual addressing.
 	 */

arch/s390/mm/pgtable.c

···
 #define ALLOC_ORDER	2
 #define FRAG_MASK	0x03
 
+unsigned int HPAGE_SHIFT;
+
 unsigned long *crst_table_alloc(struct mm_struct *mm)
 {
 	struct page *page = alloc_pages(GFP_KERNEL, ALLOC_ORDER);