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// SPDX-License-Identifier: GPL-2.0
/*
* Handling Page Tables through page fragments
*
*/
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/hugetlb.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>
void pte_frag_destroy(void *pte_frag)
{
int count;
struct page *page;
page = virt_to_page(pte_frag);
/* drop all the pending references */
count = ((unsigned long)pte_frag & ~PAGE_MASK) >> PTE_FRAG_SIZE_SHIFT;
/* We allow PTE_FRAG_NR fragments from a PTE page */
if (atomic_sub_and_test(PTE_FRAG_NR - count, &page->pt_frag_refcount)) {
pgtable_page_dtor(page);
__free_page(page);
}
}
static pte_t *get_pte_from_cache(struct mm_struct *mm)
{
void *pte_frag, *ret;
if (PTE_FRAG_NR == 1)
return NULL;
spin_lock(&mm->page_table_lock);
ret = pte_frag_get(&mm->context);
if (ret) {
pte_frag = ret + PTE_FRAG_SIZE;
/*
* If we have taken up all the fragments mark PTE page NULL
*/
if (((unsigned long)pte_frag & ~PAGE_MASK) == 0)
pte_frag = NULL;
pte_frag_set(&mm->context, pte_frag);
}
spin_unlock(&mm->page_table_lock);
return (pte_t *)ret;
}
static pte_t *__alloc_for_ptecache(struct mm_struct *mm, int kernel)
{
void *ret = NULL;
struct page *page;
if (!kernel) {
page = alloc_page(PGALLOC_GFP | __GFP_ACCOUNT);
if (!page)
return NULL;
if (!pgtable_page_ctor(page)) {
__free_page(page);
return NULL;
}
} else {
page = alloc_page(PGALLOC_GFP);
if (!page)
return NULL;
}
atomic_set(&page->pt_frag_refcount, 1);
ret = page_address(page);
/*
* if we support only one fragment just return the
* allocated page.
*/
if (PTE_FRAG_NR == 1)
return ret;
spin_lock(&mm->page_table_lock);
/*
* If we find pgtable_page set, we return
* the allocated page with single fragement
* count.
*/
if (likely(!pte_frag_get(&mm->context))) {
atomic_set(&page->pt_frag_refcount, PTE_FRAG_NR);
pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE);
}
spin_unlock(&mm->page_table_lock);
return (pte_t *)ret;
}
pte_t *pte_fragment_alloc(struct mm_struct *mm, unsigned long vmaddr, int kernel)
{
pte_t *pte;
pte = get_pte_from_cache(mm);
if (pte)
return pte;
return __alloc_for_ptecache(mm, kernel);
}
void pte_fragment_free(unsigned long *table, int kernel)
{
struct page *page = virt_to_page(table);
BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0);
if (atomic_dec_and_test(&page->pt_frag_refcount)) {
if (!kernel)
pgtable_page_dtor(page);
__free_page(page);
}
}
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