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pgtable.h

/*
 *  include/asm-s390/pgtable.h
 *
 *  S390 version
 *    Copyright (C) 1999,2000 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Hartmut Penner (hp@de.ibm.com)
 *               Ulrich Weigand (weigand@de.ibm.com)
 *               Martin Schwidefsky (schwidefsky@de.ibm.com)
 *
 *  Derived from "include/asm-i386/pgtable.h"
 */

#ifndef _ASM_S390_PGTABLE_H
#define _ASM_S390_PGTABLE_H

/*
 * The Linux memory management assumes a three-level page table setup. For
 * s390 31 bit we "fold" the mid level into the top-level page table, so
 * that we physically have the same two-level page table as the s390 mmu
 * expects in 31 bit mode. For s390 64 bit we use three of the five levels
 * the hardware provides (region first and region second tables are not
 * used).
 *
 * The "pgd_xxx()" functions are trivial for a folded two-level
 * setup: the pgd is never bad, and a pmd always exists (as it's folded
 * into the pgd entry)
 *
 * This file contains the functions and defines necessary to modify and use
 * the S390 page table tree.
 */
#ifndef __ASSEMBLY__
#include <linux/mm_types.h>
#include <asm/bug.h>
#include <asm/processor.h>

extern pgd_t swapper_pg_dir[] __attribute__ ((aligned (4096)));
extern void paging_init(void);
extern void vmem_map_init(void);

/*
 * The S390 doesn't have any external MMU info: the kernel page
 * tables contain all the necessary information.
 */
#define update_mmu_cache(vma, address, pte)     do { } while (0)

/*
 * ZERO_PAGE is a global shared page that is always zero: used
 * for zero-mapped memory areas etc..
 */
extern char empty_zero_page[PAGE_SIZE];
#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
#endif /* !__ASSEMBLY__ */

/*
 * PMD_SHIFT determines the size of the area a second-level page
 * table can map
 * PGDIR_SHIFT determines what a third-level page table entry can map
 */
#ifndef __s390x__
# define PMD_SHIFT      22
# define PUD_SHIFT      22
# define PGDIR_SHIFT    22
#else /* __s390x__ */
# define PMD_SHIFT      21
# define PUD_SHIFT      31
# define PGDIR_SHIFT    31
#endif /* __s390x__ */

#define PMD_SIZE        (1UL << PMD_SHIFT)
#define PMD_MASK        (~(PMD_SIZE-1))
#define PUD_SIZE  (1UL << PUD_SHIFT)
#define PUD_MASK  (~(PUD_SIZE-1))
#define PGDIR_SIZE      (1UL << PGDIR_SHIFT)
#define PGDIR_MASK      (~(PGDIR_SIZE-1))

/*
 * entries per page directory level: the S390 is two-level, so
 * we don't really have any PMD directory physically.
 * for S390 segment-table entries are combined to one PGD
 * that leads to 1024 pte per pgd
 */
#ifndef __s390x__
# define PTRS_PER_PTE    1024
# define PTRS_PER_PMD    1
# define PTRS_PER_PUD   1
# define PTRS_PER_PGD    512
#else /* __s390x__ */
# define PTRS_PER_PTE    512
# define PTRS_PER_PMD    1024
# define PTRS_PER_PUD   1
# define PTRS_PER_PGD    2048
#endif /* __s390x__ */

#define FIRST_USER_ADDRESS  0

#define pte_ERROR(e) \
      printk("%s:%d: bad pte %p.\n", __FILE__, __LINE__, (void *) pte_val(e))
#define pmd_ERROR(e) \
      printk("%s:%d: bad pmd %p.\n", __FILE__, __LINE__, (void *) pmd_val(e))
#define pud_ERROR(e) \
      printk("%s:%d: bad pud %p.\n", __FILE__, __LINE__, (void *) pud_val(e))
#define pgd_ERROR(e) \
      printk("%s:%d: bad pgd %p.\n", __FILE__, __LINE__, (void *) pgd_val(e))

#ifndef __ASSEMBLY__
/*
 * Just any arbitrary offset to the start of the vmalloc VM area: the
 * current 8MB value just means that there will be a 8MB "hole" after the
 * physical memory until the kernel virtual memory starts.  That means that
 * any out-of-bounds memory accesses will hopefully be caught.
 * The vmalloc() routines leaves a hole of 4kB between each vmalloced
 * area for the same reason. ;)
 * vmalloc area starts at 4GB to prevent syscall table entry exchanging
 * from modules.
 */
extern unsigned long vmalloc_end;

#ifdef CONFIG_64BIT
#define VMALLOC_ADDR    (max(0x100000000UL, (unsigned long) high_memory))
#else
#define VMALLOC_ADDR    ((unsigned long) high_memory)
#endif
#define VMALLOC_OFFSET  (8*1024*1024)
#define VMALLOC_START   ((VMALLOC_ADDR + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1))
#define VMALLOC_END     vmalloc_end

/*
 * We need some free virtual space to be able to do vmalloc.
 * VMALLOC_MIN_SIZE defines the minimum size of the vmalloc
 * area. On a machine with 2GB memory we make sure that we
 * have at least 128MB free space for vmalloc. On a machine
 * with 4TB we make sure we have at least 128GB.
 */
#ifndef __s390x__
#define VMALLOC_MIN_SIZE      0x8000000UL
#define VMALLOC_END_INIT      0x80000000UL
#else /* __s390x__ */
#define VMALLOC_MIN_SIZE      0x2000000000UL
#define VMALLOC_END_INIT      0x40000000000UL
#endif /* __s390x__ */

/*
 * A 31 bit pagetable entry of S390 has following format:
 *  |   PFRA          |    |  OS  |
 * 0                   0IP0
 * 00000000001111111111222222222233
 * 01234567890123456789012345678901
 *
 * I Page-Invalid Bit:    Page is not available for address-translation
 * P Page-Protection Bit: Store access not possible for page
 *
 * A 31 bit segmenttable entry of S390 has following format:
 *  |   P-table origin      |  |PTL
 * 0                         IC
 * 00000000001111111111222222222233
 * 01234567890123456789012345678901
 *
 * I Segment-Invalid Bit:    Segment is not available for address-translation
 * C Common-Segment Bit:     Segment is not private (PoP 3-30)
 * PTL Page-Table-Length:    Page-table length (PTL+1*16 entries -> up to 256)
 *
 * The 31 bit segmenttable origin of S390 has following format:
 *
 *  |S-table origin   |     | STL |
 * X                   **GPS
 * 00000000001111111111222222222233
 * 01234567890123456789012345678901
 *
 * X Space-Switch event:
 * G Segment-Invalid Bit:     *
 * P Private-Space Bit:       Segment is not private (PoP 3-30)
 * S Storage-Alteration:
 * STL Segment-Table-Length:  Segment-table length (STL+1*16 entries -> up to 2048)
 *
 * A 64 bit pagetable entry of S390 has following format:
 * |                     PFRA                         |0IP0|  OS  |
 * 0000000000111111111122222222223333333333444444444455555555556666
 * 0123456789012345678901234567890123456789012345678901234567890123
 *
 * I Page-Invalid Bit:    Page is not available for address-translation
 * P Page-Protection Bit: Store access not possible for page
 *
 * A 64 bit segmenttable entry of S390 has following format:
 * |        P-table origin                              |      TT
 * 0000000000111111111122222222223333333333444444444455555555556666
 * 0123456789012345678901234567890123456789012345678901234567890123
 *
 * I Segment-Invalid Bit:    Segment is not available for address-translation
 * C Common-Segment Bit:     Segment is not private (PoP 3-30)
 * P Page-Protection Bit: Store access not possible for page
 * TT Type 00
 *
 * A 64 bit region table entry of S390 has following format:
 * |        S-table origin                             |   TF  TTTL
 * 0000000000111111111122222222223333333333444444444455555555556666
 * 0123456789012345678901234567890123456789012345678901234567890123
 *
 * I Segment-Invalid Bit:    Segment is not available for address-translation
 * TT Type 01
 * TF
 * TL Table length
 *
 * The 64 bit regiontable origin of S390 has following format:
 * |      region table origon                          |       DTTL
 * 0000000000111111111122222222223333333333444444444455555555556666
 * 0123456789012345678901234567890123456789012345678901234567890123
 *
 * X Space-Switch event:
 * G Segment-Invalid Bit:  
 * P Private-Space Bit:    
 * S Storage-Alteration:
 * R Real space
 * TL Table-Length:
 *
 * A storage key has the following format:
 * | ACC |F|R|C|0|
 *  0   3 4 5 6 7
 * ACC: access key
 * F  : fetch protection bit
 * R  : referenced bit
 * C  : changed bit
 */

/* Hardware bits in the page table entry */
#define _PAGE_RO  0x200       /* HW read-only bit  */
#define _PAGE_INVALID   0x400       /* HW invalid bit    */

/* Software bits in the page table entry */
#define _PAGE_SWT 0x001       /* SW pte type bit t */
#define _PAGE_SWX 0x002       /* SW pte type bit x */

/* Six different types of pages. */
#define _PAGE_TYPE_EMPTY      0x400
#define _PAGE_TYPE_NONE       0x401
#define _PAGE_TYPE_SWAP       0x403
#define _PAGE_TYPE_FILE       0x601 /* bit 0x002 is used for offset !! */
#define _PAGE_TYPE_RO         0x200
#define _PAGE_TYPE_RW         0x000
#define _PAGE_TYPE_EX_RO      0x202
#define _PAGE_TYPE_EX_RW      0x002

/*
 * PTE type bits are rather complicated. handle_pte_fault uses pte_present,
 * pte_none and pte_file to find out the pte type WITHOUT holding the page
 * table lock. ptep_clear_flush on the other hand uses ptep_clear_flush to
 * invalidate a given pte. ipte sets the hw invalid bit and clears all tlbs
 * for the page. The page table entry is set to _PAGE_TYPE_EMPTY afterwards.
 * This change is done while holding the lock, but the intermediate step
 * of a previously valid pte with the hw invalid bit set can be observed by
 * handle_pte_fault. That makes it necessary that all valid pte types with
 * the hw invalid bit set must be distinguishable from the four pte types
 * empty, none, swap and file.
 *
 *                irxt  ipte  irxt
 * _PAGE_TYPE_EMPTY     1000   ->   1000
 * _PAGE_TYPE_NONE      1001   ->   1001
 * _PAGE_TYPE_SWAP      1011   ->   1011
 * _PAGE_TYPE_FILE      11?1   ->   11?1
 * _PAGE_TYPE_RO  0100   ->   1100
 * _PAGE_TYPE_RW  0000   ->   1000
 * _PAGE_TYPE_EX_RO     0110   ->   1110
 * _PAGE_TYPE_EX_RW     0010   ->   1010
 *
 * pte_none is true for bits combinations 1000, 1010, 1100, 1110
 * pte_present is true for bits combinations 0000, 0010, 0100, 0110, 1001
 * pte_file is true for bits combinations 1101, 1111
 * swap pte is 1011 and 0001, 0011, 0101, 0111 are invalid.
 */

#ifndef __s390x__

/* Bits in the segment table address-space-control-element */
#define _ASCE_SPACE_SWITCH    0x80000000UL      /* space switch event       */
#define _ASCE_ORIGIN_MASK     0x7ffff000UL      /* segment table origin     */
#define _ASCE_PRIVATE_SPACE   0x100 /* private space control          */
#define _ASCE_ALT_EVENT       0x80  /* storage alteration event control */
#define _ASCE_TABLE_LENGTH    0x7f  /* 128 x 64 entries = 8k          */

/* Bits in the segment table entry */
#define _SEGMENT_ENTRY_ORIGIN 0x7fffffc0UL      /* page table origin        */
#define _SEGMENT_ENTRY_INV    0x20  /* invalid segment table entry          */
#define _SEGMENT_ENTRY_COMMON 0x10  /* common segment bit             */
#define _SEGMENT_ENTRY_PTL    0x0f  /* page table length              */

#define _SEGMENT_ENTRY        (_SEGMENT_ENTRY_PTL)
#define _SEGMENT_ENTRY_EMPTY  (_SEGMENT_ENTRY_INV)

#else /* __s390x__ */

/* Bits in the segment/region table address-space-control-element */
#define _ASCE_ORIGIN          ~0xfffUL/* segment table origin               */
#define _ASCE_PRIVATE_SPACE   0x100 /* private space control          */
#define _ASCE_ALT_EVENT       0x80  /* storage alteration event control */
#define _ASCE_SPACE_SWITCH    0x40  /* space switch event             */
#define _ASCE_REAL_SPACE      0x20  /* real space control             */
#define _ASCE_TYPE_MASK       0x0c  /* asce table type mask           */
#define _ASCE_TYPE_REGION1    0x0c  /* region first table type        */
#define _ASCE_TYPE_REGION2    0x08  /* region second table type       */
#define _ASCE_TYPE_REGION3    0x04  /* region third table type        */
#define _ASCE_TYPE_SEGMENT    0x00  /* segment table type             */
#define _ASCE_TABLE_LENGTH    0x03  /* region table length            */

/* Bits in the region table entry */
#define _REGION_ENTRY_ORIGIN  ~0xfffUL/* region/segment table origin        */
#define _REGION_ENTRY_INV     0x20  /* invalid region table entry     */
#define _REGION_ENTRY_TYPE_MASK     0x0c  /* region/segment table type mask   */
#define _REGION_ENTRY_TYPE_R1 0x0c  /* region first table type        */
#define _REGION_ENTRY_TYPE_R2 0x08  /* region second table type       */
#define _REGION_ENTRY_TYPE_R3 0x04  /* region third table type        */
#define _REGION_ENTRY_LENGTH  0x03  /* region third length            */

#define _REGION1_ENTRY        (_REGION_ENTRY_TYPE_R1 | _REGION_ENTRY_LENGTH)
#define _REGION1_ENTRY_EMPTY  (_REGION_ENTRY_TYPE_R1 | _REGION_ENTRY_INV)
#define _REGION2_ENTRY        (_REGION_ENTRY_TYPE_R2 | _REGION_ENTRY_LENGTH)
#define _REGION2_ENTRY_EMPTY  (_REGION_ENTRY_TYPE_R2 | _REGION_ENTRY_INV)
#define _REGION3_ENTRY        (_REGION_ENTRY_TYPE_R3 | _REGION_ENTRY_LENGTH)
#define _REGION3_ENTRY_EMPTY  (_REGION_ENTRY_TYPE_R3 | _REGION_ENTRY_INV)

/* Bits in the segment table entry */
#define _SEGMENT_ENTRY_ORIGIN ~0x7ffUL/* segment table origin               */
#define _SEGMENT_ENTRY_RO     0x200 /* page protection bit            */
#define _SEGMENT_ENTRY_INV    0x20  /* invalid segment table entry          */

#define _SEGMENT_ENTRY        (0)
#define _SEGMENT_ENTRY_EMPTY  (_SEGMENT_ENTRY_INV)

#endif /* __s390x__ */

/*
 * A user page table pointer has the space-switch-event bit, the
 * private-space-control bit and the storage-alteration-event-control
 * bit set. A kernel page table pointer doesn't need them.
 */
#define _ASCE_USER_BITS       (_ASCE_SPACE_SWITCH | _ASCE_PRIVATE_SPACE | \
                         _ASCE_ALT_EVENT)

/* Bits int the storage key */
#define _PAGE_CHANGED    0x02          /* HW changed bit                   */
#define _PAGE_REFERENCED 0x04          /* HW referenced bit                */

/*
 * Page protection definitions.
 */
#define PAGE_NONE __pgprot(_PAGE_TYPE_NONE)
#define PAGE_RO         __pgprot(_PAGE_TYPE_RO)
#define PAGE_RW         __pgprot(_PAGE_TYPE_RW)
#define PAGE_EX_RO      __pgprot(_PAGE_TYPE_EX_RO)
#define PAGE_EX_RW      __pgprot(_PAGE_TYPE_EX_RW)

#define PAGE_KERNEL     PAGE_RW
#define PAGE_COPY PAGE_RO

/*
 * Dependent on the EXEC_PROTECT option s390 can do execute protection.
 * Write permission always implies read permission. In theory with a
 * primary/secondary page table execute only can be implemented but
 * it would cost an additional bit in the pte to distinguish all the
 * different pte types. To avoid that execute permission currently
 * implies read permission as well.
 */
         /*xwr*/
#define __P000    PAGE_NONE
#define __P001    PAGE_RO
#define __P010    PAGE_RO
#define __P011    PAGE_RO
#define __P100    PAGE_EX_RO
#define __P101    PAGE_EX_RO
#define __P110    PAGE_EX_RO
#define __P111    PAGE_EX_RO

#define __S000    PAGE_NONE
#define __S001    PAGE_RO
#define __S010    PAGE_RW
#define __S011    PAGE_RW
#define __S100    PAGE_EX_RO
#define __S101    PAGE_EX_RO
#define __S110    PAGE_EX_RW
#define __S111    PAGE_EX_RW

#ifndef __s390x__
# define PxD_SHADOW_SHIFT     1
#else /* __s390x__ */
# define PxD_SHADOW_SHIFT     2
#endif /* __s390x__ */

static inline struct page *get_shadow_page(struct page *page)
{
      if (s390_noexec && page->index)
            return virt_to_page((void *)(addr_t) page->index);
      return NULL;
}

static inline void *get_shadow_pte(void *table)
{
      unsigned long addr, offset;
      struct page *page;

      addr = (unsigned long) table;
      offset = addr & (PAGE_SIZE - 1);
      page = virt_to_page((void *)(addr ^ offset));
      return (void *)(addr_t)(page->index ? (page->index | offset) : 0UL);
}

static inline void *get_shadow_table(void *table)
{
      unsigned long addr, offset;
      struct page *page;

      addr = (unsigned long) table;
      offset = addr & ((PAGE_SIZE << PxD_SHADOW_SHIFT) - 1);
      page = virt_to_page((void *)(addr ^ offset));
      return (void *)(addr_t)(page->index ? (page->index | offset) : 0UL);
}

/*
 * Certain architectures need to do special things when PTEs
 * within a page table are directly modified.  Thus, the following
 * hook is made available.
 */
static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
                        pte_t *pteptr, pte_t pteval)
{
      pte_t *shadow_pte = get_shadow_pte(pteptr);

      *pteptr = pteval;
      if (shadow_pte) {
            if (!(pte_val(pteval) & _PAGE_INVALID) &&
                (pte_val(pteval) & _PAGE_SWX))
                  pte_val(*shadow_pte) = pte_val(pteval) | _PAGE_RO;
            else
                  pte_val(*shadow_pte) = _PAGE_TYPE_EMPTY;
      }
}

/*
 * pgd/pmd/pte query functions
 */
#ifndef __s390x__

static inline int pgd_present(pgd_t pgd) { return 1; }
static inline int pgd_none(pgd_t pgd)    { return 0; }
static inline int pgd_bad(pgd_t pgd)     { return 0; }

static inline int pud_present(pud_t pud) { return 1; }
static inline int pud_none(pud_t pud)      { return 0; }
static inline int pud_bad(pud_t pud)       { return 0; }

#else /* __s390x__ */

static inline int pgd_present(pgd_t pgd) { return 1; }
static inline int pgd_none(pgd_t pgd)      { return 0; }
static inline int pgd_bad(pgd_t pgd)       { return 0; }

static inline int pud_present(pud_t pud)
{
      return (pud_val(pud) & _REGION_ENTRY_ORIGIN) != 0UL;
}

static inline int pud_none(pud_t pud)
{
      return (pud_val(pud) & _REGION_ENTRY_INV) != 0UL;
}

static inline int pud_bad(pud_t pud)
{
      unsigned long mask = ~_REGION_ENTRY_ORIGIN & ~_REGION_ENTRY_INV;
      return (pud_val(pud) & mask) != _REGION3_ENTRY;
}

#endif /* __s390x__ */

static inline int pmd_present(pmd_t pmd)
{
      return (pmd_val(pmd) & _SEGMENT_ENTRY_ORIGIN) != 0UL;
}

static inline int pmd_none(pmd_t pmd)
{
      return (pmd_val(pmd) & _SEGMENT_ENTRY_INV) != 0UL;
}

static inline int pmd_bad(pmd_t pmd)
{
      unsigned long mask = ~_SEGMENT_ENTRY_ORIGIN & ~_SEGMENT_ENTRY_INV;
      return (pmd_val(pmd) & mask) != _SEGMENT_ENTRY;
}

static inline int pte_none(pte_t pte)
{
      return (pte_val(pte) & _PAGE_INVALID) && !(pte_val(pte) & _PAGE_SWT);
}

static inline int pte_present(pte_t pte)
{
      unsigned long mask = _PAGE_RO | _PAGE_INVALID | _PAGE_SWT | _PAGE_SWX;
      return (pte_val(pte) & mask) == _PAGE_TYPE_NONE ||
            (!(pte_val(pte) & _PAGE_INVALID) &&
             !(pte_val(pte) & _PAGE_SWT));
}

static inline int pte_file(pte_t pte)
{
      unsigned long mask = _PAGE_RO | _PAGE_INVALID | _PAGE_SWT;
      return (pte_val(pte) & mask) == _PAGE_TYPE_FILE;
}

#define __HAVE_ARCH_PTE_SAME
#define pte_same(a,b)  (pte_val(a) == pte_val(b))

/*
 * query functions pte_write/pte_dirty/pte_young only work if
 * pte_present() is true. Undefined behaviour if not..
 */
static inline int pte_write(pte_t pte)
{
      return (pte_val(pte) & _PAGE_RO) == 0;
}

static inline int pte_dirty(pte_t pte)
{
      /* A pte is neither clean nor dirty on s/390. The dirty bit
       * is in the storage key. See page_test_and_clear_dirty for
       * details.
       */
      return 0;
}

static inline int pte_young(pte_t pte)
{
      /* A pte is neither young nor old on s/390. The young bit
       * is in the storage key. See page_test_and_clear_young for
       * details.
       */
      return 0;
}

/*
 * pgd/pmd/pte modification functions
 */

#ifndef __s390x__

#define pgd_clear(pgd)        do { } while (0)
#define pud_clear(pud)        do { } while (0)

static inline void pmd_clear_kernel(pmd_t * pmdp)
{
      pmd_val(pmdp[0]) = _SEGMENT_ENTRY_EMPTY;
      pmd_val(pmdp[1]) = _SEGMENT_ENTRY_EMPTY;
      pmd_val(pmdp[2]) = _SEGMENT_ENTRY_EMPTY;
      pmd_val(pmdp[3]) = _SEGMENT_ENTRY_EMPTY;
}

#else /* __s390x__ */

#define pgd_clear(pgd)        do { } while (0)

static inline void pud_clear_kernel(pud_t *pud)
{
      pud_val(*pud) = _REGION3_ENTRY_EMPTY;
}

static inline void pud_clear(pud_t * pud)
{
      pud_t *shadow = get_shadow_table(pud);

      pud_clear_kernel(pud);
      if (shadow)
            pud_clear_kernel(shadow);
}

static inline void pmd_clear_kernel(pmd_t * pmdp)
{
      pmd_val(*pmdp) = _SEGMENT_ENTRY_EMPTY;
      pmd_val1(*pmdp) = _SEGMENT_ENTRY_EMPTY;
}

#endif /* __s390x__ */

static inline void pmd_clear(pmd_t * pmdp)
{
      pmd_t *shadow_pmd = get_shadow_table(pmdp);

      pmd_clear_kernel(pmdp);
      if (shadow_pmd)
            pmd_clear_kernel(shadow_pmd);
}

static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
      pte_t *shadow_pte = get_shadow_pte(ptep);

      pte_val(*ptep) = _PAGE_TYPE_EMPTY;
      if (shadow_pte)
            pte_val(*shadow_pte) = _PAGE_TYPE_EMPTY;
}

/*
 * The following pte modification functions only work if
 * pte_present() is true. Undefined behaviour if not..
 */
static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
{
      pte_val(pte) &= PAGE_MASK;
      pte_val(pte) |= pgprot_val(newprot);
      return pte;
}

static inline pte_t pte_wrprotect(pte_t pte)
{
      /* Do not clobber _PAGE_TYPE_NONE pages!  */
      if (!(pte_val(pte) & _PAGE_INVALID))
            pte_val(pte) |= _PAGE_RO;
      return pte;
}

static inline pte_t pte_mkwrite(pte_t pte)
{
      pte_val(pte) &= ~_PAGE_RO;
      return pte;
}

static inline pte_t pte_mkclean(pte_t pte)
{
      /* The only user of pte_mkclean is the fork() code.
         We must *not* clear the *physical* page dirty bit
         just because fork() wants to clear the dirty bit in
         *one* of the page's mappings.  So we just do nothing. */
      return pte;
}

static inline pte_t pte_mkdirty(pte_t pte)
{
      /* We do not explicitly set the dirty bit because the
       * sske instruction is slow. It is faster to let the
       * next instruction set the dirty bit.
       */
      return pte;
}

static inline pte_t pte_mkold(pte_t pte)
{
      /* S/390 doesn't keep its dirty/referenced bit in the pte.
       * There is no point in clearing the real referenced bit.
       */
      return pte;
}

static inline pte_t pte_mkyoung(pte_t pte)
{
      /* S/390 doesn't keep its dirty/referenced bit in the pte.
       * There is no point in setting the real referenced bit.
       */
      return pte;
}

#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
                                  unsigned long addr, pte_t *ptep)
{
      return 0;
}

#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
                               unsigned long address, pte_t *ptep)
{
      /* No need to flush TLB; bits are in storage key */
      return 0;
}

static inline void __ptep_ipte(unsigned long address, pte_t *ptep)
{
      if (!(pte_val(*ptep) & _PAGE_INVALID)) {
#ifndef __s390x__
            /* S390 has 1mb segments, we are emulating 4MB segments */
            pte_t *pto = (pte_t *) (((unsigned long) ptep) & 0x7ffffc00);
#else
            /* ipte in zarch mode can do the math */
            pte_t *pto = ptep;
#endif
            asm volatile(
                  "     ipte  %2,%3"
                  : "=m" (*ptep) : "m" (*ptep),
                    "a" (pto), "a" (address));
      }
      pte_val(*ptep) = _PAGE_TYPE_EMPTY;
}

static inline void ptep_invalidate(unsigned long address, pte_t *ptep)
{
      __ptep_ipte(address, ptep);
      ptep = get_shadow_pte(ptep);
      if (ptep)
            __ptep_ipte(address, ptep);
}

/*
 * This is hard to understand. ptep_get_and_clear and ptep_clear_flush
 * both clear the TLB for the unmapped pte. The reason is that
 * ptep_get_and_clear is used in common code (e.g. change_pte_range)
 * to modify an active pte. The sequence is
 *   1) ptep_get_and_clear
 *   2) set_pte_at
 *   3) flush_tlb_range
 * On s390 the tlb needs to get flushed with the modification of the pte
 * if the pte is active. The only way how this can be implemented is to
 * have ptep_get_and_clear do the tlb flush. In exchange flush_tlb_range
 * is a nop.
 */
#define __HAVE_ARCH_PTEP_GET_AND_CLEAR
#define ptep_get_and_clear(__mm, __address, __ptep)               \
({                                                    \
      pte_t __pte = *(__ptep);                              \
      if (atomic_read(&(__mm)->mm_users) > 1 ||             \
          (__mm) != current->active_mm)                     \
            ptep_invalidate(__address, __ptep);             \
      else                                            \
            pte_clear((__mm), (__address), (__ptep));       \
      __pte;                                                \
})

#define __HAVE_ARCH_PTEP_CLEAR_FLUSH
static inline pte_t ptep_clear_flush(struct vm_area_struct *vma,
                             unsigned long address, pte_t *ptep)
{
      pte_t pte = *ptep;
      ptep_invalidate(address, ptep);
      return pte;
}

/*
 * The batched pte unmap code uses ptep_get_and_clear_full to clear the
 * ptes. Here an optimization is possible. tlb_gather_mmu flushes all
 * tlbs of an mm if it can guarantee that the ptes of the mm_struct
 * cannot be accessed while the batched unmap is running. In this case
 * full==1 and a simple pte_clear is enough. See tlb.h.
 */
#define __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL
static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
                                  unsigned long addr,
                                  pte_t *ptep, int full)
{
      pte_t pte = *ptep;

      if (full)
            pte_clear(mm, addr, ptep);
      else
            ptep_invalidate(addr, ptep);
      return pte;
}

#define __HAVE_ARCH_PTEP_SET_WRPROTECT
#define ptep_set_wrprotect(__mm, __addr, __ptep)                  \
({                                                    \
      pte_t __pte = *(__ptep);                              \
      if (pte_write(__pte)) {                               \
            if (atomic_read(&(__mm)->mm_users) > 1 ||       \
                (__mm) != current->active_mm)               \
                  ptep_invalidate(__addr, __ptep);          \
            set_pte_at(__mm, __addr, __ptep, pte_wrprotect(__pte));     \
      }                                               \
})

#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
#define ptep_set_access_flags(__vma, __addr, __ptep, __entry, __dirty)  \
({                                                    \
      int __changed = !pte_same(*(__ptep), __entry);              \
      if (__changed) {                                \
            ptep_invalidate(__addr, __ptep);                \
            set_pte_at((__vma)->vm_mm, __addr, __ptep, __entry);  \
      }                                               \
      __changed;                                      \
})

/*
 * Test and clear dirty bit in storage key.
 * We can't clear the changed bit atomically. This is a potential
 * race against modification of the referenced bit. This function
 * should therefore only be called if it is not mapped in any
 * address space.
 */
#define __HAVE_ARCH_PAGE_TEST_DIRTY
static inline int page_test_dirty(struct page *page)
{
      return (page_get_storage_key(page_to_phys(page)) & _PAGE_CHANGED) != 0;
}

#define __HAVE_ARCH_PAGE_CLEAR_DIRTY
static inline void page_clear_dirty(struct page *page)
{
      page_set_storage_key(page_to_phys(page), PAGE_DEFAULT_KEY);
}

/*
 * Test and clear referenced bit in storage key.
 */
#define __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
static inline int page_test_and_clear_young(struct page *page)
{
      unsigned long physpage = page_to_phys(page);
      int ccode;

      asm volatile(
            "     rrbe  0,%1\n"
            "     ipm   %0\n"
            "     srl   %0,28\n"
            : "=d" (ccode) : "a" (physpage) : "cc" );
      return ccode & 2;
}

/*
 * Conversion functions: convert a page and protection to a page entry,
 * and a page entry and page directory to the page they refer to.
 */
static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
{
      pte_t __pte;
      pte_val(__pte) = physpage + pgprot_val(pgprot);
      return __pte;
}

static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
{
      unsigned long physpage = page_to_phys(page);

      return mk_pte_phys(physpage, pgprot);
}

#define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
#define pud_index(address) (((address) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
#define pmd_index(address) (((address) >> PMD_SHIFT) & (PTRS_PER_PMD-1))
#define pte_index(address) (((address) >> PAGE_SHIFT) & (PTRS_PER_PTE-1))

#define pgd_offset(mm, address) ((mm)->pgd + pgd_index(address))
#define pgd_offset_k(address) pgd_offset(&init_mm, address)

#ifndef __s390x__

#define pmd_deref(pmd) (pmd_val(pmd) & _SEGMENT_ENTRY_ORIGIN)
#define pud_deref(pmd) ({ BUG(); 0UL; })
#define pgd_deref(pmd) ({ BUG(); 0UL; })

#define pud_offset(pgd, address) ((pud_t *) pgd)
#define pmd_offset(pud, address) ((pmd_t *) pud + pmd_index(address))

#else /* __s390x__ */

#define pmd_deref(pmd) (pmd_val(pmd) & _SEGMENT_ENTRY_ORIGIN)
#define pud_deref(pud) (pud_val(pud) & _REGION_ENTRY_ORIGIN)
#define pgd_deref(pgd) ({ BUG(); 0UL; })

#define pud_offset(pgd, address) ((pud_t *) pgd)

static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
{
      pmd_t *pmd = (pmd_t *) pud_deref(*pud);
      return pmd + pmd_index(address);
}

#endif /* __s390x__ */

#define pfn_pte(pfn,pgprot) mk_pte_phys(__pa((pfn) << PAGE_SHIFT),(pgprot))
#define pte_pfn(x) (pte_val(x) >> PAGE_SHIFT)
#define pte_page(x) pfn_to_page(pte_pfn(x))

#define pmd_page(pmd) pfn_to_page(pmd_val(pmd) >> PAGE_SHIFT)

/* Find an entry in the lowest level page table.. */
#define pte_offset(pmd, addr) ((pte_t *) pmd_deref(*(pmd)) + pte_index(addr))
#define pte_offset_kernel(pmd, address) pte_offset(pmd,address)
#define pte_offset_map(pmd, address) pte_offset_kernel(pmd, address)
#define pte_offset_map_nested(pmd, address) pte_offset_kernel(pmd, address)
#define pte_unmap(pte) do { } while (0)
#define pte_unmap_nested(pte) do { } while (0)

/*
 * 31 bit swap entry format:
 * A page-table entry has some bits we have to treat in a special way.
 * Bits 0, 20 and bit 23 have to be zero, otherwise an specification
 * exception will occur instead of a page translation exception. The
 * specifiation exception has the bad habit not to store necessary
 * information in the lowcore.
 * Bit 21 and bit 22 are the page invalid bit and the page protection
 * bit. We set both to indicate a swapped page.
 * Bit 30 and 31 are used to distinguish the different page types. For
 * a swapped page these bits need to be zero.
 * This leaves the bits 1-19 and bits 24-29 to store type and offset.
 * We use the 5 bits from 25-29 for the type and the 20 bits from 1-19
 * plus 24 for the offset.
 * 0|     offset        |0110|o|type |00|
 * 0 0000000001111111111 2222 2 22222 33
 * 0 1234567890123456789 0123 4 56789 01
 *
 * 64 bit swap entry format:
 * A page-table entry has some bits we have to treat in a special way.
 * Bits 52 and bit 55 have to be zero, otherwise an specification
 * exception will occur instead of a page translation exception. The
 * specifiation exception has the bad habit not to store necessary
 * information in the lowcore.
 * Bit 53 and bit 54 are the page invalid bit and the page protection
 * bit. We set both to indicate a swapped page.
 * Bit 62 and 63 are used to distinguish the different page types. For
 * a swapped page these bits need to be zero.
 * This leaves the bits 0-51 and bits 56-61 to store type and offset.
 * We use the 5 bits from 57-61 for the type and the 53 bits from 0-51
 * plus 56 for the offset.
 * |                      offset                        |0110|o|type |00|
 *  0000000000111111111122222222223333333333444444444455 5555 5 55566 66
 *  0123456789012345678901234567890123456789012345678901 2345 6 78901 23
 */
#ifndef __s390x__
#define __SWP_OFFSET_MASK (~0UL >> 12)
#else
#define __SWP_OFFSET_MASK (~0UL >> 11)
#endif
static inline pte_t mk_swap_pte(unsigned long type, unsigned long offset)
{
      pte_t pte;
      offset &= __SWP_OFFSET_MASK;
      pte_val(pte) = _PAGE_TYPE_SWAP | ((type & 0x1f) << 2) |
            ((offset & 1UL) << 7) | ((offset & ~1UL) << 11);
      return pte;
}

#define __swp_type(entry)     (((entry).val >> 2) & 0x1f)
#define __swp_offset(entry)   (((entry).val >> 11) | (((entry).val >> 7) & 1))
#define __swp_entry(type,offset) ((swp_entry_t) { pte_val(mk_swap_pte((type),(offset))) })

#define __pte_to_swp_entry(pte)     ((swp_entry_t) { pte_val(pte) })
#define __swp_entry_to_pte(x) ((pte_t) { (x).val })

#ifndef __s390x__
# define PTE_FILE_MAX_BITS    26
#else /* __s390x__ */
# define PTE_FILE_MAX_BITS    59
#endif /* __s390x__ */

#define pte_to_pgoff(__pte) \
      ((((__pte).pte >> 12) << 7) + (((__pte).pte >> 1) & 0x7f))

#define pgoff_to_pte(__off) \
      ((pte_t) { ((((__off) & 0x7f) << 1) + (((__off) >> 7) << 12)) \
               | _PAGE_TYPE_FILE })

#endif /* !__ASSEMBLY__ */

#define kern_addr_valid(addr)   (1)

extern int add_shared_memory(unsigned long start, unsigned long size);
extern int remove_shared_memory(unsigned long start, unsigned long size);

/*
 * No page table caches to initialise
 */
#define pgtable_cache_init()  do { } while (0)

#define __HAVE_ARCH_MEMMAP_INIT
extern void memmap_init(unsigned long, int, unsigned long, unsigned long);

#include <asm-generic/pgtable.h>

#endif /* _S390_PAGE_H */

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