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>

diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
index ab89ea4f941492901d215893a4b1c1b56ebef2f4..150aa326afff119ccc0e41e089e0539a821e99bb 100644 (file)
--- a/arch/sh/mm/Makefile
+++ b/arch/sh/mm/Makefile
@@ -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)

diff --git a/arch/sh/mm/gup.c b/arch/sh/mm/gup.c
new file mode 100644 (file)
index 0000000..bf8daf9
--- /dev/null
+++ b/arch/sh/mm/gup.c
@@ -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;
+       }
+}