arch/x86/mm/pgtable.c - kernel/msm-5.4 - Gitiles

 #include <linux/mm.h>
 #include <linux/gfp.h>
 #include <asm/pgalloc.h>
 #include <asm/pgtable.h>
 #include <asm/tlb.h>
 #include <asm/fixmap.h>

 #define PGALLOC_GFP GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO

 #ifdef CONFIG_HIGHPTE
 #define PGALLOC_USER_GFP __GFP_HIGHMEM
 #else
 #define PGALLOC_USER_GFP 0
 #endif

 gfp_t __userpte_alloc_gfp = PGALLOC_GFP | PGALLOC_USER_GFP;

 pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
 {
 	return (pte_t *)__get_free_page(PGALLOC_GFP);
 }

 pgtable_t pte_alloc_one(struct mm_struct *mm, unsigned long address)
 {
 	struct page *pte;

 	pte = alloc_pages(__userpte_alloc_gfp, 0);
 	if (!pte)
 		return NULL;
 	if (!pgtable_page_ctor(pte)) {
 		__free_page(pte);
 		return NULL;
 	}
 	return pte;
 }

 static int __init setup_userpte(char *arg)
 {
 	if (!arg)
 		return -EINVAL;

 	/*
 	 * "userpte=nohigh" disables allocation of user pagetables in
 	 * high memory.
 	 */
 	if (strcmp(arg, "nohigh") == 0)
 		__userpte_alloc_gfp &= ~__GFP_HIGHMEM;
 	else
 		return -EINVAL;
 	return 0;
 }
 early_param("userpte", setup_userpte);

 void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
 {
 	pgtable_page_dtor(pte);
 	paravirt_release_pte(page_to_pfn(pte));
 	tlb_remove_page(tlb, pte);
 }

 #if PAGETABLE_LEVELS > 2
 void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
 {
 	struct page *page = virt_to_page(pmd);
 	paravirt_release_pmd(__pa(pmd) >> PAGE_SHIFT);
 	/*
 	 * NOTE! For PAE, any changes to the top page-directory-pointer-table
 	 * entries need a full cr3 reload to flush.
 	 */
 #ifdef CONFIG_X86_PAE
 	tlb->need_flush_all = 1;
 #endif
 	pgtable_pmd_page_dtor(page);
 	tlb_remove_page(tlb, page);
 }

 #if PAGETABLE_LEVELS > 3
 void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
 {
 	paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
 	tlb_remove_page(tlb, virt_to_page(pud));
 }
 #endif	/* PAGETABLE_LEVELS > 3 */
 #endif	/* PAGETABLE_LEVELS > 2 */

 static inline void pgd_list_add(pgd_t *pgd)
 {
 	struct page *page = virt_to_page(pgd);

 	list_add(&page->lru, &pgd_list);
 }

 static inline void pgd_list_del(pgd_t *pgd)
 {
 	struct page *page = virt_to_page(pgd);

 	list_del(&page->lru);
 }

 #define UNSHARED_PTRS_PER_PGD				\
 	(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)


 static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
 {
 	BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
 	virt_to_page(pgd)->index = (pgoff_t)mm;
 }

 struct mm_struct *pgd_page_get_mm(struct page *page)
 {
 	return (struct mm_struct *)page->index;
 }

 static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
 {
 	/* If the pgd points to a shared pagetable level (either the
 	   ptes in non-PAE, or shared PMD in PAE), then just copy the
 	   references from swapper_pg_dir. */
 	if (PAGETABLE_LEVELS == 2 ||
 	    (PAGETABLE_LEVELS == 3 && SHARED_KERNEL_PMD) ||
 	    PAGETABLE_LEVELS == 4) {
 		clone_pgd_range(pgd + KERNEL_PGD_BOUNDARY,
 				swapper_pg_dir + KERNEL_PGD_BOUNDARY,
 				KERNEL_PGD_PTRS);
 	}

 	/* list required to sync kernel mapping updates */
 	if (!SHARED_KERNEL_PMD) {
 		pgd_set_mm(pgd, mm);
 		pgd_list_add(pgd);
 	}
 }

 static void pgd_dtor(pgd_t *pgd)
 {
 	if (SHARED_KERNEL_PMD)
 		return;

 	spin_lock(&pgd_lock);
 	pgd_list_del(pgd);
 	spin_unlock(&pgd_lock);
 }

 /*
  * List of all pgd's needed for non-PAE so it can invalidate entries
  * in both cached and uncached pgd's; not needed for PAE since the
  * kernel pmd is shared. If PAE were not to share the pmd a similar
  * tactic would be needed. This is essentially codepath-based locking
  * against pageattr.c; it is the unique case in which a valid change
  * of kernel pagetables can't be lazily synchronized by vmalloc faults.
  * vmalloc faults work because attached pagetables are never freed.
  * -- nyc
  */

 #ifdef CONFIG_X86_PAE
 /*
  * In PAE mode, we need to do a cr3 reload (=tlb flush) when
  * updating the top-level pagetable entries to guarantee the
  * processor notices the update.  Since this is expensive, and
  * all 4 top-level entries are used almost immediately in a
  * new process's life, we just pre-populate them here.
  *
  * Also, if we're in a paravirt environment where the kernel pmd is
  * not shared between pagetables (!SHARED_KERNEL_PMDS), we allocate
  * and initialize the kernel pmds here.
  */
 #define PREALLOCATED_PMDS	UNSHARED_PTRS_PER_PGD

 void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
 {
 	paravirt_alloc_pmd(mm, __pa(pmd) >> PAGE_SHIFT);

 	/* Note: almost everything apart from _PAGE_PRESENT is
 	   reserved at the pmd (PDPT) level. */
 	set_pud(pudp, __pud(__pa(pmd) | _PAGE_PRESENT));

 	/*
 	 * According to Intel App note "TLBs, Paging-Structure Caches,
 	 * and Their Invalidation", April 2007, document 317080-001,
 	 * section 8.1: in PAE mode we explicitly have to flush the
 	 * TLB via cr3 if the top-level pgd is changed...
 	 */
 	flush_tlb_mm(mm);
 }
 #else  /* !CONFIG_X86_PAE */

 /* No need to prepopulate any pagetable entries in non-PAE modes. */
 #define PREALLOCATED_PMDS	0

 #endif	/* CONFIG_X86_PAE */

 static void free_pmds(pmd_t *pmds[])
 {
 	int i;

 	for(i = 0; i < PREALLOCATED_PMDS; i++)
 		if (pmds[i]) {
 			pgtable_pmd_page_dtor(virt_to_page(pmds[i]));
 			free_page((unsigned long)pmds[i]);
 		}
 }

 static int preallocate_pmds(pmd_t *pmds[])
 {
 	int i;
 	bool failed = false;

 	for(i = 0; i < PREALLOCATED_PMDS; i++) {
 		pmd_t *pmd = (pmd_t *)__get_free_page(PGALLOC_GFP);
 		if (!pmd)
 			failed = true;
 		if (pmd && !pgtable_pmd_page_ctor(virt_to_page(pmd))) {
 			free_page((unsigned long)pmd);
 			pmd = NULL;
 			failed = true;
 		}
 		pmds[i] = pmd;
 	}

 	if (failed) {
 		free_pmds(pmds);
 		return -ENOMEM;
 	}

 	return 0;
 }

 /*
  * Mop up any pmd pages which may still be attached to the pgd.
  * Normally they will be freed by munmap/exit_mmap, but any pmd we
  * preallocate which never got a corresponding vma will need to be
  * freed manually.
  */
 static void pgd_mop_up_pmds(struct mm_struct *mm, pgd_t *pgdp)
 {
 	int i;

 	for(i = 0; i < PREALLOCATED_PMDS; i++) {
 		pgd_t pgd = pgdp[i];

 		if (pgd_val(pgd) != 0) {
 			pmd_t *pmd = (pmd_t *)pgd_page_vaddr(pgd);

 			pgdp[i] = native_make_pgd(0);

 			paravirt_release_pmd(pgd_val(pgd) >> PAGE_SHIFT);
 			pmd_free(mm, pmd);
 		}
 	}
 }

 static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[])
 {
 	pud_t *pud;
 	int i;

 	if (PREALLOCATED_PMDS == 0) /* Work around gcc-3.4.x bug */
 		return;

 	pud = pud_offset(pgd, 0);

 	for (i = 0; i < PREALLOCATED_PMDS; i++, pud++) {
 		pmd_t *pmd = pmds[i];

 		if (i >= KERNEL_PGD_BOUNDARY)
 			memcpy(pmd, (pmd_t *)pgd_page_vaddr(swapper_pg_dir[i]),
 			       sizeof(pmd_t) * PTRS_PER_PMD);

 		pud_populate(mm, pud, pmd);
 	}
 }

 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *pgd;
 	pmd_t *pmds[PREALLOCATED_PMDS];

 	pgd = (pgd_t *)__get_free_page(PGALLOC_GFP);

 	if (pgd == NULL)
 		goto out;

 	mm->pgd = pgd;

 	if (preallocate_pmds(pmds) != 0)
 		goto out_free_pgd;

 	if (paravirt_pgd_alloc(mm) != 0)
 		goto out_free_pmds;

 	/*
 	 * Make sure that pre-populating the pmds is atomic with
 	 * respect to anything walking the pgd_list, so that they
 	 * never see a partially populated pgd.
 	 */
 	spin_lock(&pgd_lock);

 	pgd_ctor(mm, pgd);
 	pgd_prepopulate_pmd(mm, pgd, pmds);

 	spin_unlock(&pgd_lock);

 	return pgd;

 out_free_pmds:
 	free_pmds(pmds);
 out_free_pgd:
 	free_page((unsigned long)pgd);
 out:
 	return NULL;
 }

 void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
 	pgd_mop_up_pmds(mm, pgd);
 	pgd_dtor(pgd);
 	paravirt_pgd_free(mm, pgd);
 	free_page((unsigned long)pgd);
 }

 /*
  * Used to set accessed or dirty bits in the page table entries
  * on other architectures. On x86, the accessed and dirty bits
  * are tracked by hardware. However, do_wp_page calls this function
  * to also make the pte writeable at the same time the dirty bit is
  * set. In that case we do actually need to write the PTE.
  */
 int ptep_set_access_flags(struct vm_area_struct *vma,
 			  unsigned long address, pte_t *ptep,
 			  pte_t entry, int dirty)
 {
 	int changed = !pte_same(*ptep, entry);

 	if (changed && dirty) {
 		*ptep = entry;
 		pte_update_defer(vma->vm_mm, address, ptep);
 	}

 	return changed;
 }

 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pmdp_set_access_flags(struct vm_area_struct *vma,
 			  unsigned long address, pmd_t *pmdp,
 			  pmd_t entry, int dirty)
 {
 	int changed = !pmd_same(*pmdp, entry);

 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

 	if (changed && dirty) {
 		*pmdp = entry;
 		pmd_update_defer(vma->vm_mm, address, pmdp);
 		/*
 		 * We had a write-protection fault here and changed the pmd
 		 * to to more permissive. No need to flush the TLB for that,
 		 * #PF is architecturally guaranteed to do that and in the
 		 * worst-case we'll generate a spurious fault.
 		 */
 	}

 	return changed;
 }
 #endif

 int ptep_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pte_t *ptep)
 {
 	int ret = 0;

 	if (pte_young(*ptep))
 		ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
 					 (unsigned long *) &ptep->pte);

 	if (ret)
 		pte_update(vma->vm_mm, addr, ptep);

 	return ret;
 }

 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pmd_t *pmdp)
 {
 	int ret = 0;

 	if (pmd_young(*pmdp))
 		ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
 					 (unsigned long *)pmdp);

 	if (ret)
 		pmd_update(vma->vm_mm, addr, pmdp);

 	return ret;
 }
 #endif

 int ptep_clear_flush_young(struct vm_area_struct *vma,
 			   unsigned long address, pte_t *ptep)
 {
 	/*
 	 * On x86 CPUs, clearing the accessed bit without a TLB flush
 	 * doesn't cause data corruption. [ It could cause incorrect
 	 * page aging and the (mistaken) reclaim of hot pages, but the
 	 * chance of that should be relatively low. ]
 	 *
 	 * So as a performance optimization don't flush the TLB when
 	 * clearing the accessed bit, it will eventually be flushed by
 	 * a context switch or a VM operation anyway. [ In the rare
 	 * event of it not getting flushed for a long time the delay
 	 * shouldn't really matter because there's no real memory
 	 * pressure for swapout to react to. ]
 	 */
 	return ptep_test_and_clear_young(vma, address, ptep);
 }

 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pmdp_clear_flush_young(struct vm_area_struct *vma,
 			   unsigned long address, pmd_t *pmdp)
 {
 	int young;

 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

 	young = pmdp_test_and_clear_young(vma, address, pmdp);
 	if (young)
 		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);

 	return young;
 }

 void pmdp_splitting_flush(struct vm_area_struct *vma,
 			  unsigned long address, pmd_t *pmdp)
 {
 	int set;
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	set = !test_and_set_bit(_PAGE_BIT_SPLITTING,
 				(unsigned long *)pmdp);
 	if (set) {
 		pmd_update(vma->vm_mm, address, pmdp);
 		/* need tlb flush only to serialize against gup-fast */
 		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 	}
 }
 #endif

 /**
  * reserve_top_address - reserves a hole in the top of kernel address space
  * @reserve - size of hole to reserve
  *
  * Can be used to relocate the fixmap area and poke a hole in the top
  * of kernel address space to make room for a hypervisor.
  */
 void __init reserve_top_address(unsigned long reserve)
 {
 #ifdef CONFIG_X86_32
 	BUG_ON(fixmaps_set > 0);
 	printk(KERN_INFO "Reserving virtual address space above 0x%08x\n",
 	       (int)-reserve);
 	__FIXADDR_TOP = -reserve - PAGE_SIZE;
 #endif
 }

 int fixmaps_set;

 void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
 {
 	unsigned long address = __fix_to_virt(idx);

 	if (idx >= __end_of_fixed_addresses) {
 		BUG();
 		return;
 	}
 	set_pte_vaddr(address, pte);
 	fixmaps_set++;
 }

 void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
 		       pgprot_t flags)
 {
 	__native_set_fixmap(idx, pfn_pte(phys >> PAGE_SHIFT, flags));
 }
	#include <linux/mm.h>
	#include <linux/gfp.h>
	#include <asm/pgalloc.h>
	#include <asm/pgtable.h>
	#include <asm/tlb.h>
	#include <asm/fixmap.h>

	#define PGALLOC_GFP GFP_KERNEL \| __GFP_NOTRACK \| __GFP_REPEAT \| __GFP_ZERO

	#ifdef CONFIG_HIGHPTE
	#define PGALLOC_USER_GFP __GFP_HIGHMEM
	#else
	#define PGALLOC_USER_GFP 0
	#endif

	gfp_t __userpte_alloc_gfp = PGALLOC_GFP \| PGALLOC_USER_GFP;

	pte_t pte_alloc_one_kernel(struct mm_struct mm, unsigned long address)
	{
	return (pte_t *)__get_free_page(PGALLOC_GFP);
	}

	pgtable_t pte_alloc_one(struct mm_struct *mm, unsigned long address)
	{
	struct page *pte;

	pte = alloc_pages(__userpte_alloc_gfp, 0);
	if (!pte)
	return NULL;
	if (!pgtable_page_ctor(pte)) {
	__free_page(pte);
	return NULL;
	}
	return pte;
	}

	static int __init setup_userpte(char *arg)
	{
	if (!arg)
	return -EINVAL;

	/*
	* "userpte=nohigh" disables allocation of user pagetables in
	* high memory.
	*/
	if (strcmp(arg, "nohigh") == 0)
	__userpte_alloc_gfp &= ~__GFP_HIGHMEM;
	else
	return -EINVAL;
	return 0;
	}
	early_param("userpte", setup_userpte);

	void ___pte_free_tlb(struct mmu_gather tlb, struct page pte)
	{
	pgtable_page_dtor(pte);
	paravirt_release_pte(page_to_pfn(pte));
	tlb_remove_page(tlb, pte);
	}

	#if PAGETABLE_LEVELS > 2
	void ___pmd_free_tlb(struct mmu_gather tlb, pmd_t pmd)
	{
	struct page *page = virt_to_page(pmd);
	paravirt_release_pmd(__pa(pmd) >> PAGE_SHIFT);
	/*
	* NOTE! For PAE, any changes to the top page-directory-pointer-table
	* entries need a full cr3 reload to flush.
	*/
	#ifdef CONFIG_X86_PAE
	tlb->need_flush_all = 1;
	#endif
	pgtable_pmd_page_dtor(page);
	tlb_remove_page(tlb, page);
	}

	#if PAGETABLE_LEVELS > 3
	void ___pud_free_tlb(struct mmu_gather tlb, pud_t pud)
	{
	paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
	tlb_remove_page(tlb, virt_to_page(pud));
	}
	#endif /* PAGETABLE_LEVELS > 3 */
	#endif /* PAGETABLE_LEVELS > 2 */

	static inline void pgd_list_add(pgd_t *pgd)
	{
	struct page *page = virt_to_page(pgd);

	list_add(&page->lru, &pgd_list);
	}

	static inline void pgd_list_del(pgd_t *pgd)
	{
	struct page *page = virt_to_page(pgd);

	list_del(&page->lru);
	}

	#define UNSHARED_PTRS_PER_PGD \
	(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)


	static void pgd_set_mm(pgd_t pgd, struct mm_struct mm)
	{
	BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
	virt_to_page(pgd)->index = (pgoff_t)mm;
	}

	struct mm_struct pgd_page_get_mm(struct page page)
	{
	return (struct mm_struct *)page->index;
	}

	static void pgd_ctor(struct mm_struct mm, pgd_t pgd)
	{
	/* If the pgd points to a shared pagetable level (either the
	ptes in non-PAE, or shared PMD in PAE), then just copy the
	references from swapper_pg_dir. */
	if (PAGETABLE_LEVELS == 2 \|\|
	(PAGETABLE_LEVELS == 3 && SHARED_KERNEL_PMD) \|\|
	PAGETABLE_LEVELS == 4) {
	clone_pgd_range(pgd + KERNEL_PGD_BOUNDARY,
	swapper_pg_dir + KERNEL_PGD_BOUNDARY,
	KERNEL_PGD_PTRS);
	}

	/* list required to sync kernel mapping updates */
	if (!SHARED_KERNEL_PMD) {
	pgd_set_mm(pgd, mm);
	pgd_list_add(pgd);
	}
	}

	static void pgd_dtor(pgd_t *pgd)
	{
	if (SHARED_KERNEL_PMD)
	return;

	spin_lock(&pgd_lock);
	pgd_list_del(pgd);
	spin_unlock(&pgd_lock);
	}

	/*
	* List of all pgd's needed for non-PAE so it can invalidate entries
	* in both cached and uncached pgd's; not needed for PAE since the
	* kernel pmd is shared. If PAE were not to share the pmd a similar
	* tactic would be needed. This is essentially codepath-based locking
	* against pageattr.c; it is the unique case in which a valid change
	* of kernel pagetables can't be lazily synchronized by vmalloc faults.
	* vmalloc faults work because attached pagetables are never freed.
	* -- nyc
	*/

	#ifdef CONFIG_X86_PAE
	/*
	* In PAE mode, we need to do a cr3 reload (=tlb flush) when
	* updating the top-level pagetable entries to guarantee the
	* processor notices the update. Since this is expensive, and
	* all 4 top-level entries are used almost immediately in a
	* new process's life, we just pre-populate them here.
	*
	* Also, if we're in a paravirt environment where the kernel pmd is
	* not shared between pagetables (!SHARED_KERNEL_PMDS), we allocate
	* and initialize the kernel pmds here.
	*/
	#define PREALLOCATED_PMDS UNSHARED_PTRS_PER_PGD

	void pud_populate(struct mm_struct mm, pud_t pudp, pmd_t *pmd)
	{
	paravirt_alloc_pmd(mm, __pa(pmd) >> PAGE_SHIFT);

	/* Note: almost everything apart from _PAGE_PRESENT is
	reserved at the pmd (PDPT) level. */
	set_pud(pudp, __pud(__pa(pmd) \| _PAGE_PRESENT));

	/*
	* According to Intel App note "TLBs, Paging-Structure Caches,
	* and Their Invalidation", April 2007, document 317080-001,
	* section 8.1: in PAE mode we explicitly have to flush the
	* TLB via cr3 if the top-level pgd is changed...
	*/
	flush_tlb_mm(mm);
	}
	#else /* !CONFIG_X86_PAE */

	/* No need to prepopulate any pagetable entries in non-PAE modes. */
	#define PREALLOCATED_PMDS 0

	#endif /* CONFIG_X86_PAE */

	static void free_pmds(pmd_t *pmds[])
	{
	int i;

	for(i = 0; i < PREALLOCATED_PMDS; i++)
	if (pmds[i]) {
	pgtable_pmd_page_dtor(virt_to_page(pmds[i]));
	free_page((unsigned long)pmds[i]);
	}
	}

	static int preallocate_pmds(pmd_t *pmds[])
	{
	int i;
	bool failed = false;

	for(i = 0; i < PREALLOCATED_PMDS; i++) {
	pmd_t pmd = (pmd_t )__get_free_page(PGALLOC_GFP);
	if (!pmd)
	failed = true;
	if (pmd && !pgtable_pmd_page_ctor(virt_to_page(pmd))) {
	free_page((unsigned long)pmd);
	pmd = NULL;
	failed = true;
	}
	pmds[i] = pmd;
	}

	if (failed) {
	free_pmds(pmds);
	return -ENOMEM;
	}

	return 0;
	}

	/*
	* Mop up any pmd pages which may still be attached to the pgd.
	* Normally they will be freed by munmap/exit_mmap, but any pmd we
	* preallocate which never got a corresponding vma will need to be
	* freed manually.
	*/
	static void pgd_mop_up_pmds(struct mm_struct mm, pgd_t pgdp)
	{
	int i;

	for(i = 0; i < PREALLOCATED_PMDS; i++) {
	pgd_t pgd = pgdp[i];

	if (pgd_val(pgd) != 0) {
	pmd_t pmd = (pmd_t )pgd_page_vaddr(pgd);

	pgdp[i] = native_make_pgd(0);

	paravirt_release_pmd(pgd_val(pgd) >> PAGE_SHIFT);
	pmd_free(mm, pmd);
	}
	}
	}

	static void pgd_prepopulate_pmd(struct mm_struct mm, pgd_t pgd, pmd_t *pmds[])
	{
	pud_t *pud;
	int i;

	if (PREALLOCATED_PMDS == 0) /* Work around gcc-3.4.x bug */
	return;

	pud = pud_offset(pgd, 0);

	for (i = 0; i < PREALLOCATED_PMDS; i++, pud++) {
	pmd_t *pmd = pmds[i];

	if (i >= KERNEL_PGD_BOUNDARY)
	memcpy(pmd, (pmd_t *)pgd_page_vaddr(swapper_pg_dir[i]),
	sizeof(pmd_t) * PTRS_PER_PMD);

	pud_populate(mm, pud, pmd);
	}
	}

	pgd_t pgd_alloc(struct mm_struct mm)
	{
	pgd_t *pgd;
	pmd_t *pmds[PREALLOCATED_PMDS];

	pgd = (pgd_t *)__get_free_page(PGALLOC_GFP);

	if (pgd == NULL)
	goto out;

	mm->pgd = pgd;

	if (preallocate_pmds(pmds) != 0)
	goto out_free_pgd;

	if (paravirt_pgd_alloc(mm) != 0)
	goto out_free_pmds;

	/*
	* Make sure that pre-populating the pmds is atomic with
	* respect to anything walking the pgd_list, so that they
	* never see a partially populated pgd.
	*/
	spin_lock(&pgd_lock);

	pgd_ctor(mm, pgd);
	pgd_prepopulate_pmd(mm, pgd, pmds);

	spin_unlock(&pgd_lock);

	return pgd;

	out_free_pmds:
	free_pmds(pmds);
	out_free_pgd:
	free_page((unsigned long)pgd);
	out:
	return NULL;
	}

	void pgd_free(struct mm_struct mm, pgd_t pgd)
	{
	pgd_mop_up_pmds(mm, pgd);
	pgd_dtor(pgd);
	paravirt_pgd_free(mm, pgd);
	free_page((unsigned long)pgd);
	}

	/*
	* Used to set accessed or dirty bits in the page table entries
	* on other architectures. On x86, the accessed and dirty bits
	* are tracked by hardware. However, do_wp_page calls this function
	* to also make the pte writeable at the same time the dirty bit is
	* set. In that case we do actually need to write the PTE.
	*/
	int ptep_set_access_flags(struct vm_area_struct *vma,
	unsigned long address, pte_t *ptep,
	pte_t entry, int dirty)
	{
	int changed = !pte_same(*ptep, entry);

	if (changed && dirty) {
	*ptep = entry;
	pte_update_defer(vma->vm_mm, address, ptep);
	}

	return changed;
	}

	#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	int pmdp_set_access_flags(struct vm_area_struct *vma,
	unsigned long address, pmd_t *pmdp,
	pmd_t entry, int dirty)
	{
	int changed = !pmd_same(*pmdp, entry);

	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

	if (changed && dirty) {
	*pmdp = entry;
	pmd_update_defer(vma->vm_mm, address, pmdp);
	/*
	* We had a write-protection fault here and changed the pmd
	* to to more permissive. No need to flush the TLB for that,
	* #PF is architecturally guaranteed to do that and in the
	* worst-case we'll generate a spurious fault.
	*/
	}

	return changed;
	}
	#endif

	int ptep_test_and_clear_young(struct vm_area_struct *vma,
	unsigned long addr, pte_t *ptep)
	{
	int ret = 0;

	if (pte_young(*ptep))
	ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
	(unsigned long *) &ptep->pte);

	if (ret)
	pte_update(vma->vm_mm, addr, ptep);

	return ret;
	}

	#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	int pmdp_test_and_clear_young(struct vm_area_struct *vma,
	unsigned long addr, pmd_t *pmdp)
	{
	int ret = 0;

	if (pmd_young(*pmdp))
	ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
	(unsigned long *)pmdp);

	if (ret)
	pmd_update(vma->vm_mm, addr, pmdp);

	return ret;
	}
	#endif

	int ptep_clear_flush_young(struct vm_area_struct *vma,
	unsigned long address, pte_t *ptep)
	{
	/*
	* On x86 CPUs, clearing the accessed bit without a TLB flush
	* doesn't cause data corruption. [ It could cause incorrect
	* page aging and the (mistaken) reclaim of hot pages, but the
	* chance of that should be relatively low. ]
	*
	* So as a performance optimization don't flush the TLB when
	* clearing the accessed bit, it will eventually be flushed by
	* a context switch or a VM operation anyway. [ In the rare
	* event of it not getting flushed for a long time the delay
	* shouldn't really matter because there's no real memory
	* pressure for swapout to react to. ]
	*/
	return ptep_test_and_clear_young(vma, address, ptep);
	}

	#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	int pmdp_clear_flush_young(struct vm_area_struct *vma,
	unsigned long address, pmd_t *pmdp)
	{
	int young;

	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

	young = pmdp_test_and_clear_young(vma, address, pmdp);
	if (young)
	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);

	return young;
	}

	void pmdp_splitting_flush(struct vm_area_struct *vma,
	unsigned long address, pmd_t *pmdp)
	{
	int set;
	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
	set = !test_and_set_bit(_PAGE_BIT_SPLITTING,
	(unsigned long *)pmdp);
	if (set) {
	pmd_update(vma->vm_mm, address, pmdp);
	/* need tlb flush only to serialize against gup-fast */
	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
	}
	}
	#endif

	/**
	* reserve_top_address - reserves a hole in the top of kernel address space
	* @reserve - size of hole to reserve
	*
	* Can be used to relocate the fixmap area and poke a hole in the top
	* of kernel address space to make room for a hypervisor.
	*/
	void __init reserve_top_address(unsigned long reserve)
	{
	#ifdef CONFIG_X86_32
	BUG_ON(fixmaps_set > 0);
	printk(KERN_INFO "Reserving virtual address space above 0x%08x\n",
	(int)-reserve);
	__FIXADDR_TOP = -reserve - PAGE_SIZE;
	#endif
	}

	int fixmaps_set;

	void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
	{
	unsigned long address = __fix_to_virt(idx);

	if (idx >= __end_of_fixed_addresses) {
	BUG();
	return;
	}
	set_pte_vaddr(address, pte);
	fixmaps_set++;
	}

	void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
	pgprot_t flags)
	{
	__native_set_fixmap(idx, pfn_pte(phys >> PAGE_SHIFT, flags));
	}