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sh: lockless get_user_pages_fast() 

Implement get_user_pages_fast without locking in the fastpath on sh.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This commit is contained in:
Paul Mundt 2010-10-27 16:43:08 +09:00
parent a16382ce1c
commit 667b279baa
2 changed files with 274 additions and 1 deletions
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2
arch/sh/mm/Makefile
View File

@ -15,7 +15,7 @@ cacheops-$(CONFIG_CPU_SHX3) += cache-shx3.o
obj-y += $(cacheops-y)
mmu-y := nommu.o extable_32.o
mmu-$(CONFIG_MMU) := extable_$(BITS).o fault_$(BITS).o \
mmu-$(CONFIG_MMU) := extable_$(BITS).o fault_$(BITS).o gup.o \
ioremap.o kmap.o pgtable.o tlbflush_$(BITS).o
obj-y += $(mmu-y)

273
arch/sh/mm/gup.c Normal file
View File

@ -0,0 +1,273 @@
/*
* Lockless get_user_pages_fast for SuperH
*
* Copyright (C) 2009 - 2010 Paul Mundt
*
* Cloned from the x86 and PowerPC versions, by:
*
* Copyright (C) 2008 Nick Piggin
* Copyright (C) 2008 Novell Inc.
*/
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/highmem.h>
#include <asm/pgtable.h>
static inline pte_t gup_get_pte(pte_t *ptep)
{
#ifndef CONFIG_X2TLB
return ACCESS_ONCE(*ptep);
#else
/*
* With get_user_pages_fast, we walk down the pagetables without
* taking any locks. For this we would like to load the pointers
* atomically, but that is not possible with 64-bit PTEs. What
* we do have is the guarantee that a pte will only either go
* from not present to present, or present to not present or both
* -- it will not switch to a completely different present page
* without a TLB flush in between; something that we are blocking
* by holding interrupts off.
*
* Setting ptes from not present to present goes:
* ptep->pte_high = h;
* smp_wmb();
* ptep->pte_low = l;
*
* And present to not present goes:
* ptep->pte_low = 0;
* smp_wmb();
* ptep->pte_high = 0;
*
* We must ensure here that the load of pte_low sees l iff pte_high
* sees h. We load pte_high *after* loading pte_low, which ensures we
* don't see an older value of pte_high. *Then* we recheck pte_low,
* which ensures that we haven't picked up a changed pte high. We might
* have got rubbish values from pte_low and pte_high, but we are
* guaranteed that pte_low will not have the present bit set *unless*
* it is 'l'. And get_user_pages_fast only operates on present ptes, so
* we're safe.
*
* gup_get_pte should not be used or copied outside gup.c without being
* very careful -- it does not atomically load the pte or anything that
* is likely to be useful for you.
*/
pte_t pte;
retry:
pte.pte_low = ptep->pte_low;
smp_rmb();
pte.pte_high = ptep->pte_high;
smp_rmb();
if (unlikely(pte.pte_low != ptep->pte_low))
goto retry;
return pte;
#endif
}
/*
* 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)
{
u64 mask, result;
pte_t *ptep;
#ifdef CONFIG_X2TLB
result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
if (write)
result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
#elif defined(CONFIG_SUPERH64)
result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
if (write)
result |= _PAGE_WRITE;
#else
result = _PAGE_PRESENT | _PAGE_USER;
if (write)
result |= _PAGE_RW;
#endif
mask = result | _PAGE_SPECIAL;
ptep = pte_offset_map(&pmd, addr);
do {
pte_t pte = gup_get_pte(ptep);
struct page *page;
if ((pte_val(pte) & mask) != result) {
pte_unmap(ptep);
return 0;
}
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
get_page(page);
pages[*nr] = page;
(*nr)++;
} while (ptep++, addr += PAGE_SIZE, addr != end);
pte_unmap(ptep - 1);
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))
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;
}
/*
* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
* back to the regular GUP.
*/
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;
unsigned long flags;
pgd_t *pgdp;
int nr = 0;
start &= PAGE_MASK;
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
(void __user *)start, len)))
return 0;
/*
* This doesn't prevent pagetable teardown, but does prevent
* the pagetables and pages from being freed.
*/
local_irq_save(flags);
pgdp = pgd_offset(mm, addr);
do {
pgd_t pgd = *pgdp;
next = pgd_addr_end(addr, end);
if (pgd_none(pgd))
break;
if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
break;
} while (pgdp++, addr = next, addr != end);
local_irq_restore(flags);
return nr;
}
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @write: whether pages will be written to
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
*
* Attempt to pin user pages in memory without taking mm->mmap_sem.
* If not successful, it will fall back to taking the lock and
* calling get_user_pages().
*
* Returns number of pages pinned. This may be fewer than the number
* requested. If nr_pages is 0 or negative, returns 0. If no pages
* were pinned, returns -errno.
*/
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;
if (end < start)
goto slow_irqon;
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();
slow_irqon:
/* 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;
}
}