/*
* Lockless get_user_pages_fast for powerpc
*
* Copyright (C) 2008 Nick Piggin
* Copyright (C) 2008 Novell Inc.
*/
#undef DEBUG
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/hugetlb.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;
result = _PAGE_PRESENT|_PAGE_USER;
if (write)
result |= _PAGE_RW;
mask = result | _PAGE_SPECIAL;
ptep = pte_offset_kernel(&pmd, addr);
do {
pte_t pte = *ptep;
struct page *page;
if ((pte_val(pte) & mask) != result)
return 0;
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
if (!page_cache_get_speculative(page))
return 0;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(page);
return 0;
}
pages[*nr] = page;
(*nr)++;
} while (ptep++, addr += PAGE_SIZE, addr != end);
return 1;
}
#ifdef CONFIG_HUGETLB_PAGE
static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
unsigned long *addr, unsigned long end,
int write, struct page **pages, int *nr)
{
unsigned long mask;
unsigned long pte_end;
struct page *head, *page;
pte_t pte;
int refs;
pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
if (pte_end < end)
end = pte_end;
pte = *ptep;
mask = _PAGE_PRESENT|_PAGE_USER;
if (write)
mask |= _PAGE_RW;
if ((pte_val(pte) & mask) != mask)
return 0;
/* hugepages are never "special" */
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
refs = 0;
head = pte_page(pte);
page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
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(pte_val(pte) != pte_val(*ptep))) {
/* Could be optimized better */
while (*nr) {
put_page(page);
(*nr)--;
}
}
return 1;
}
#endif /* CONFIG_HUGETLB_PAGE */
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))
return 0;
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 psize, nr = 0;
unsigned int shift;
pr_debug("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
start &= PAGE_MASK;
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
start, len)))
goto slow_irqon;
pr_debug(" aligned: %lx .. %lx\n", start, end);
#ifdef CONFIG_HUGETLB_PAGE
/* We bail out on slice boundary crossing when hugetlb is
* enabled in order to not have to deal with two different
* page table formats
*/
if (addr < SLICE_LOW_TOP) {
if (end > SLICE_LOW_TOP)
goto slow_irqon;
if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
GET_LOW_SLICE_INDEX(end - 1)))
goto slow_irqon;
} else {
if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
GET_HIGH_SLICE_INDEX(end - 1)))
goto slow_irqon;
}
#endif /* CONFIG_HUGETLB_PAGE */
/*
* 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 powerpc.
*
* 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();
psize = get_slice_psize(mm, addr);
shift = mmu_psize_defs[psize].shift;
#ifdef CONFIG_HUGETLB_PAGE
if (unlikely(mmu_huge_psizes[psize])) {
pte_t *ptep;
unsigned long a = addr;
unsigned long sz = ((1UL) << shift);
struct hstate *hstate = size_to_hstate(sz);
BUG_ON(!hstate);
/*
* XXX: could be optimized to avoid hstate
* lookup entirely (just use shift)
*/
do {
VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
ptep = huge_pte_offset(mm, a);
pr_debug(" %016lx: huge ptep %p\n", a, ptep);
if (!ptep || !gup_huge_pte(ptep, hstate, &a, end, write, pages,
&nr))
goto slow;
} while (a != end);
} else
#endif /* CONFIG_HUGETLB_PAGE */
{
pgdp = pgd_offset(mm, addr);
do {
pgd_t pgd = *pgdp;
VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
pr_debug(" %016lx: normal pgd %p\n", addr,
(void *)pgd_val(pgd));
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();
slow_irqon:
pr_debug(" slow path ! nr = %d\n", nr);
/* 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;
}
}
