root/arch/powerpc/mm/pgtable-frag.c

DEFINITIONS

1. pte_frag_destroy
2. get_pte_from_cache
3. __alloc_for_ptecache
4. pte_fragment_alloc
5. pte_fragment_free

   1 // SPDX-License-Identifier: GPL-2.0
   2 
   3 /*
   4  *  Handling Page Tables through page fragments
   5  *
   6  */
   7 
   8 #include <linux/kernel.h>
   9 #include <linux/gfp.h>
  10 #include <linux/mm.h>
  11 #include <linux/percpu.h>
  12 #include <linux/hardirq.h>
  13 #include <linux/hugetlb.h>
  14 #include <asm/pgalloc.h>
  15 #include <asm/tlbflush.h>
  16 #include <asm/tlb.h>
  17 
  18 void pte_frag_destroy(void *pte_frag)
  19 {
  20         int count;
  21         struct page *page;
  22 
  23         page = virt_to_page(pte_frag);
  24         /* drop all the pending references */
  25         count = ((unsigned long)pte_frag & ~PAGE_MASK) >> PTE_FRAG_SIZE_SHIFT;
  26         /* We allow PTE_FRAG_NR fragments from a PTE page */
  27         if (atomic_sub_and_test(PTE_FRAG_NR - count, &page->pt_frag_refcount)) {
  28                 pgtable_pte_page_dtor(page);
  29                 __free_page(page);
  30         }
  31 }
  32 
  33 static pte_t *get_pte_from_cache(struct mm_struct *mm)
  34 {
  35         void *pte_frag, *ret;
  36 
  37         if (PTE_FRAG_NR == 1)
  38                 return NULL;
  39 
  40         spin_lock(&mm->page_table_lock);
  41         ret = pte_frag_get(&mm->context);
  42         if (ret) {
  43                 pte_frag = ret + PTE_FRAG_SIZE;
  44                 /*
  45                  * If we have taken up all the fragments mark PTE page NULL
  46                  */
  47                 if (((unsigned long)pte_frag & ~PAGE_MASK) == 0)
  48                         pte_frag = NULL;
  49                 pte_frag_set(&mm->context, pte_frag);
  50         }
  51         spin_unlock(&mm->page_table_lock);
  52         return (pte_t *)ret;
  53 }
  54 
  55 static pte_t *__alloc_for_ptecache(struct mm_struct *mm, int kernel)
  56 {
  57         void *ret = NULL;
  58         struct page *page;
  59 
  60         if (!kernel) {
  61                 page = alloc_page(PGALLOC_GFP | __GFP_ACCOUNT);
  62                 if (!page)
  63                         return NULL;
  64                 if (!pgtable_pte_page_ctor(page)) {
  65                         __free_page(page);
  66                         return NULL;
  67                 }
  68         } else {
  69                 page = alloc_page(PGALLOC_GFP);
  70                 if (!page)
  71                         return NULL;
  72         }
  73 
  74         atomic_set(&page->pt_frag_refcount, 1);
  75 
  76         ret = page_address(page);
  77         /*
  78          * if we support only one fragment just return the
  79          * allocated page.
  80          */
  81         if (PTE_FRAG_NR == 1)
  82                 return ret;
  83         spin_lock(&mm->page_table_lock);
  84         /*
  85          * If we find pgtable_page set, we return
  86          * the allocated page with single fragement
  87          * count.
  88          */
  89         if (likely(!pte_frag_get(&mm->context))) {
  90                 atomic_set(&page->pt_frag_refcount, PTE_FRAG_NR);
  91                 pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE);
  92         }
  93         spin_unlock(&mm->page_table_lock);
  94 
  95         return (pte_t *)ret;
  96 }
  97 
  98 pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel)
  99 {
 100         pte_t *pte;
 101 
 102         pte = get_pte_from_cache(mm);
 103         if (pte)
 104                 return pte;
 105 
 106         return __alloc_for_ptecache(mm, kernel);
 107 }
 108 
 109 void pte_fragment_free(unsigned long *table, int kernel)
 110 {
 111         struct page *page = virt_to_page(table);
 112 
 113         BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0);
 114         if (atomic_dec_and_test(&page->pt_frag_refcount)) {
 115                 if (!kernel)
 116                         pgtable_pte_page_dtor(page);
 117                 __free_page(page);
 118         }
 119 }