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/*
* Lockless get_user_pages_fast for sparc, cribbed from powerpc
*
* Copyright (C) 2008 Nick Piggin
* Copyright (C) 2008 Novell Inc.
*/
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/pagemap.h>
#include <linux/rwsem.h>
#include <asm/pgtable.h>
/*
* The performance critical leaf functions are made noinline otherwise gcc
* inlines everything into a single function which results in too much
* register pressure.
*/
static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
unsigned long mask, result;
pte_t *ptep;
if (tlb_type == hypervisor) {
result = _PAGE_PRESENT_4V|_PAGE_P_4V;
if (write)
result |= _PAGE_WRITE_4V;
} else {
result = _PAGE_PRESENT_4U|_PAGE_P_4U;
if (write)
result |= _PAGE_WRITE_4U;
}
mask = result | _PAGE_SPECIAL;
ptep = pte_offset_kernel(&pmd, addr);
do {
struct page *page, *head;
pte_t pte = *ptep;
if ((pte_val(pte) & mask) != result)
return 0;
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
/* The hugepage case is simplified on sparc64 because
* we encode the sub-page pfn offsets into the
* hugepage PTEs. We could optimize this in the future
* use page_cache_add_speculative() for the hugepage case.
*/
page = pte_page(pte);
head = compound_head(page);
if (!page_cache_get_speculative(head))
return 0;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(head);
return 0;
}
if (head != page)
get_huge_page_tail(page);
pages[*nr] = page;
(*nr)++;
} while (ptep++, addr += PAGE_SIZE, addr != end);
return 1;
}
static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages,
int *nr)
{
struct page *head, *page, *tail;
int refs;
if (!pmd_large(pmd))
return 0;
if (write && !pmd_write(pmd))
return 0;
refs = 0;
head = pmd_page(pmd);
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
tail = page;
do {
VM_BUG_ON(compound_head(page) != head);
pages[*nr] = page;
(*nr)++;
page++;
refs++;
} while (addr += PAGE_SIZE, addr != end);
if (!page_cache_add_speculative(head, refs)) {
*nr -= refs;
return 0;
}
if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
*nr -= refs;
while (refs--)
put_page(head);
return 0;
}
/* Any tail page need their mapcount reference taken before we
* return.
*/
while (refs--) {
if (PageTail(tail))
get_huge_page_tail(tail);
tail++;
}
return 1;
}
static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
int write, struct page **pages, int *nr)
{
unsigned long next;
pmd_t *pmdp;
pmdp = pmd_offset(&pud, addr);
do {
pmd_t pmd = *pmdp;
next = pmd_addr_end(addr, end);
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0;
if (unlikely(pmd_large(pmd))) {
if (!gup_huge_pmd(pmdp, pmd, addr, next,
write, pages, nr))
return 0;
} else if (!gup_pte_range(pmd, addr, next, write,
pages, nr))
return 0;
} while (pmdp++, addr = next, addr != end);
return 1;
}
static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
int write, struct page **pages, int *nr)
{
unsigned long next;
pud_t *pudp;
pudp = pud_offset(&pgd, addr);
do {
pud_t pud = *pudp;
next = pud_addr_end(addr, end);
if (pud_none(pud))
return 0;
if (!gup_pmd_range(pud, addr, next, write, pages, nr))
return 0;
} while (pudp++, addr = next, addr != end);
return 1;
}
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
struct mm_struct *mm = current->mm;
unsigned long addr, len, end;
unsigned long next;
pgd_t *pgdp;
int nr = 0;
start &= PAGE_MASK;
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
/*
* XXX: batch / limit 'nr', to avoid large irq off latency
* needs some instrumenting to determine the common sizes used by
* important workloads (eg. DB2), and whether limiting the batch size
* will decrease performance.
*
* It seems like we're in the clear for the moment. Direct-IO is
* the main guy that batches up lots of get_user_pages, and even
* they are limited to 64-at-a-time which is not so many.
*/
/*
* This doesn't prevent pagetable teardown, but does prevent
* the pagetables from being freed on sparc.
*
* So long as we atomically load page table pointers versus teardown,
* we can follow the address down to the the page and take a ref on it.
*/
local_irq_disable();
pgdp = pgd_offset(mm, addr);
do {
pgd_t pgd = *pgdp;
next = pgd_addr_end(addr, end);
if (pgd_none(pgd))
goto slow;
if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
goto slow;
} while (pgdp++, addr = next, addr != end);
local_irq_enable();
VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
return nr;
{
int ret;
slow:
local_irq_enable();
/* Try to get the remaining pages with get_user_pages */
start += nr << PAGE_SHIFT;
pages += nr;
down_read(&mm->mmap_sem);
ret = get_user_pages(current, mm, start,
(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
up_read(&mm->mmap_sem);
/* Have to be a bit careful with return values */
if (nr > 0) {
if (ret < 0)
ret = nr;
else
ret += nr;
}
return ret;
}
}
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