[S390] lockless get_user_pages_fast()

Implement get_user_pages_fast without locking in the fastpath on s390.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

5 files changed, 381 insertions, 21 deletions

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index eec054484419..6fbc6f3fbdf2 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -3,6 +3,6 @@
 #
 
 obj-y    := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
-            page-states.o
+            page-states.o gup.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
new file mode 100644
index 000000000000..38e641cdd977
--- /dev/null
+++ b/arch/s390/mm/gup.c
@@ -0,0 +1,225 @@
+/*
+ *  Lockless get_user_pages_fast for s390
+ *
+ *  Copyright IBM Corp. 2010
+ *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
+ */
+#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 inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
+                unsigned long end, int write, struct page **pages, int *nr)
+{
+        unsigned long mask, result;
+        pte_t *ptep, pte;
+        struct page *page;
+
+        result = write ? 0 : _PAGE_RO;
+        mask = result | _PAGE_INVALID | _PAGE_SPECIAL;
+
+        ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
+        do {
+                pte = *ptep;
+                barrier();
+                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;
+}
+
+static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
+                unsigned long end, int write, struct page **pages, int *nr)
+{
+        unsigned long mask, result;
+        struct page *head, *page;
+        int refs;
+
+        result = write ? 0 : _SEGMENT_ENTRY_RO;
+        mask = result | _SEGMENT_ENTRY_INV;
+        if ((pmd_val(pmd) & mask) != result)
+                return 0;
+        VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
+
+        refs = 0;
+        head = pmd_page(pmd);
+        page = head + ((addr & ~PMD_MASK) >> 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(pmd_val(pmd) != pmd_val(*pmdp))) {
+                *nr -= refs;
+                while (refs--)
+                        put_page(head);
+        }
+
+        return 1;
+}
+
+
+static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
+                unsigned long end, int write, struct page **pages, int *nr)
+{
+        unsigned long next;
+        pmd_t *pmdp, pmd;
+
+        pmdp = (pmd_t *) pudp;
+#ifdef CONFIG_64BIT
+        if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
+                pmdp = (pmd_t *) pud_deref(pud);
+        pmdp += pmd_index(addr);
+#endif
+        do {
+                pmd = *pmdp;
+                barrier();
+                next = pmd_addr_end(addr, end);
+                if (pmd_none(pmd))
+                        return 0;
+                if (unlikely(pmd_huge(pmd))) {
+                        if (!gup_huge_pmd(pmdp, pmd, addr, next,
+                                          write, pages, nr))
+                                return 0;
+                } else if (!gup_pte_range(pmdp, pmd, addr, next,
+                                          write, pages, nr))
+                        return 0;
+        } while (pmdp++, addr = next, addr != end);
+
+        return 1;
+}
+
+static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
+                unsigned long end, int write, struct page **pages, int *nr)
+{
+        unsigned long next;
+        pud_t *pudp, pud;
+
+        pudp = (pud_t *) pgdp;
+#ifdef CONFIG_64BIT
+        if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
+                pudp = (pud_t *) pgd_deref(pgd);
+        pudp += pud_index(addr);
+#endif
+        do {
+                pud = *pudp;
+                barrier();
+                next = pud_addr_end(addr, end);
+                if (pud_none(pud))
+                        return 0;
+                if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
+                        return 0;
+        } while (pudp++, addr = next, addr != end);
+
+        return 1;
+}
+
+/**
+ * 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, pgd;
+        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() doesn't prevent pagetable teardown, but does
+         * prevent the pagetables from being freed on s390.
+         *
+         * 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 = *pgdp;
+                barrier();
+                next = pgd_addr_end(addr, end);
+                if (pgd_none(pgd))
+                        goto slow;
+                if (!gup_pud_range(pgdp, 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;
+        }
+}
diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
index f28c43d2f61d..639cd21f2218 100644
--- a/arch/s390/mm/hugetlbpage.c
+++ b/arch/s390/mm/hugetlbpage.c
@@ -68,7 +68,7 @@ void arch_release_hugepage(struct page *page)
         ptep = (pte_t *) page[1].index;
         if (!ptep)
                 return;
-        pte_free(&init_mm, ptep);
+        page_table_free(&init_mm, (unsigned long *) ptep);
         page[1].index = 0;
 }
 
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 0744fb3536b1..852a3fec1ece 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -38,8 +38,6 @@
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __attribute__((__aligned__(PAGE_SIZE)));
 
 unsigned long empty_zero_page, zero_page_mask;
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 8d999249d357..19338d228c9b 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -15,6 +15,7 @@
 #include <linux/spinlock.h>
 #include <linux/module.h>
 #include <linux/quicklist.h>
+#include <linux/rcupdate.h>
 
 #include <asm/system.h>
 #include <asm/pgtable.h>
@@ -23,6 +24,67 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 
+struct rcu_table_freelist {
+        struct rcu_head rcu;
+        struct mm_struct *mm;
+        unsigned int pgt_index;
+        unsigned int crst_index;
+        unsigned long *table[0];
+};
+
+#define RCU_FREELIST_SIZE \
+        ((PAGE_SIZE - sizeof(struct rcu_table_freelist)) \
+          / sizeof(unsigned long))
+
+DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
+static DEFINE_PER_CPU(struct rcu_table_freelist *, rcu_table_freelist);
+
+static void __page_table_free(struct mm_struct *mm, unsigned long *table);
+static void __crst_table_free(struct mm_struct *mm, unsigned long *table);
+
+static struct rcu_table_freelist *rcu_table_freelist_get(struct mm_struct *mm)
+{
+        struct rcu_table_freelist **batchp = &__get_cpu_var(rcu_table_freelist);
+        struct rcu_table_freelist *batch = *batchp;
+
+        if (batch)
+                return batch;
+        batch = (struct rcu_table_freelist *) __get_free_page(GFP_ATOMIC);
+        if (batch) {
+                batch->mm = mm;
+                batch->pgt_index = 0;
+                batch->crst_index = RCU_FREELIST_SIZE;
+                *batchp = batch;
+        }
+        return batch;
+}
+
+static void rcu_table_freelist_callback(struct rcu_head *head)
+{
+        struct rcu_table_freelist *batch =
+                container_of(head, struct rcu_table_freelist, rcu);
+
+        while (batch->pgt_index > 0)
+                __page_table_free(batch->mm, batch->table[--batch->pgt_index]);
+        while (batch->crst_index < RCU_FREELIST_SIZE)
+                __crst_table_free(batch->mm, batch->table[batch->crst_index++]);
+        free_page((unsigned long) batch);
+}
+
+void rcu_table_freelist_finish(void)
+{
+        struct rcu_table_freelist *batch = __get_cpu_var(rcu_table_freelist);
+
+        if (!batch)
+                return;
+        call_rcu(&batch->rcu, rcu_table_freelist_callback);
+        __get_cpu_var(rcu_table_freelist) = NULL;
+}
+
+static void smp_sync(void *arg)
+{
+}
+
 #ifndef CONFIG_64BIT
 #define ALLOC_ORDER     1
 #define TABLES_PER_PAGE 4
@@ -78,25 +140,55 @@ unsigned long *crst_table_alloc(struct mm_struct *mm, int noexec)
                 }
                 page->index = page_to_phys(shadow);
         }
-        spin_lock(&mm->context.list_lock);
+        spin_lock_bh(&mm->context.list_lock);
         list_add(&page->lru, &mm->context.crst_list);
-        spin_unlock(&mm->context.list_lock);
+        spin_unlock_bh(&mm->context.list_lock);
         return (unsigned long *) page_to_phys(page);
 }
 
-void crst_table_free(struct mm_struct *mm, unsigned long *table)
+static void __crst_table_free(struct mm_struct *mm, unsigned long *table)
 {
         unsigned long *shadow = get_shadow_table(table);
-        struct page *page = virt_to_page(table);
 
-        spin_lock(&mm->context.list_lock);
-        list_del(&page->lru);
-        spin_unlock(&mm->context.list_lock);
         if (shadow)
                 free_pages((unsigned long) shadow, ALLOC_ORDER);
         free_pages((unsigned long) table, ALLOC_ORDER);
 }
 
+void crst_table_free(struct mm_struct *mm, unsigned long *table)
+{
+        struct page *page = virt_to_page(table);
+
+        spin_lock_bh(&mm->context.list_lock);
+        list_del(&page->lru);
+        spin_unlock_bh(&mm->context.list_lock);
+        __crst_table_free(mm, table);
+}
+
+void crst_table_free_rcu(struct mm_struct *mm, unsigned long *table)
+{
+        struct rcu_table_freelist *batch;
+        struct page *page = virt_to_page(table);
+
+        spin_lock_bh(&mm->context.list_lock);
+        list_del(&page->lru);
+        spin_unlock_bh(&mm->context.list_lock);
+        if (atomic_read(&mm->mm_users) < 2 &&
+            cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
+                __crst_table_free(mm, table);
+                return;
+        }
+        batch = rcu_table_freelist_get(mm);
+        if (!batch) {
+                smp_call_function(smp_sync, NULL, 1);
+                __crst_table_free(mm, table);
+                return;
+        }
+        batch->table[--batch->crst_index] = table;
+        if (batch->pgt_index >= batch->crst_index)
+                rcu_table_freelist_finish();
+}
+
 #ifdef CONFIG_64BIT
 int crst_table_upgrade(struct mm_struct *mm, unsigned long limit)
 {
@@ -108,7 +200,7 @@ repeat:
         table = crst_table_alloc(mm, mm->context.noexec);
         if (!table)
                 return -ENOMEM;
-        spin_lock(&mm->page_table_lock);
+        spin_lock_bh(&mm->page_table_lock);
         if (mm->context.asce_limit < limit) {
                 pgd = (unsigned long *) mm->pgd;
                 if (mm->context.asce_limit <= (1UL << 31)) {
@@ -130,7 +222,7 @@ repeat:
                 mm->task_size = mm->context.asce_limit;
                 table = NULL;
         }
-        spin_unlock(&mm->page_table_lock);
+        spin_unlock_bh(&mm->page_table_lock);
         if (table)
                 crst_table_free(mm, table);
         if (mm->context.asce_limit < limit)
@@ -182,7 +274,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
         unsigned long bits;
 
         bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
-        spin_lock(&mm->context.list_lock);
+        spin_lock_bh(&mm->context.list_lock);
         page = NULL;
         if (!list_empty(&mm->context.pgtable_list)) {
                 page = list_first_entry(&mm->context.pgtable_list,
@@ -191,7 +283,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
                         page = NULL;
         }
         if (!page) {
-                spin_unlock(&mm->context.list_lock);
+                spin_unlock_bh(&mm->context.list_lock);
                 page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
                 if (!page)
                         return NULL;
@@ -202,7 +294,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
                         clear_table_pgstes(table);
                 else
                         clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
-                spin_lock(&mm->context.list_lock);
+                spin_lock_bh(&mm->context.list_lock);
                 list_add(&page->lru, &mm->context.pgtable_list);
         }
         table = (unsigned long *) page_to_phys(page);
@@ -213,10 +305,25 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
         page->flags |= bits;
         if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
                 list_move_tail(&page->lru, &mm->context.pgtable_list);
-        spin_unlock(&mm->context.list_lock);
+        spin_unlock_bh(&mm->context.list_lock);
         return table;
 }
 
+static void __page_table_free(struct mm_struct *mm, unsigned long *table)
+{
+        struct page *page;
+        unsigned long bits;
+
+        bits = ((unsigned long) table) & 15;
+        table = (unsigned long *)(((unsigned long) table) ^ bits);
+        page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
+        page->flags ^= bits;
+        if (!(page->flags & FRAG_MASK)) {
+                pgtable_page_dtor(page);
+                __free_page(page);
+        }
+}
+
 void page_table_free(struct mm_struct *mm, unsigned long *table)
 {
         struct page *page;
@@ -225,7 +332,7 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
         bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
         bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
-        spin_lock(&mm->context.list_lock);
+        spin_lock_bh(&mm->context.list_lock);
         page->flags ^= bits;
         if (page->flags & FRAG_MASK) {
                 /* Page now has some free pgtable fragments. */
@@ -234,18 +341,48 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
         } else
                 /* All fragments of the 4K page have been freed. */
                 list_del(&page->lru);
-        spin_unlock(&mm->context.list_lock);
+        spin_unlock_bh(&mm->context.list_lock);
         if (page) {
                 pgtable_page_dtor(page);
                 __free_page(page);
         }
 }
 
+void page_table_free_rcu(struct mm_struct *mm, unsigned long *table)
+{
+        struct rcu_table_freelist *batch;
+        struct page *page;
+        unsigned long bits;
+
+        if (atomic_read(&mm->mm_users) < 2 &&
+            cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
+                page_table_free(mm, table);
+                return;
+        }
+        batch = rcu_table_freelist_get(mm);
+        if (!batch) {
+                smp_call_function(smp_sync, NULL, 1);
+                page_table_free(mm, table);
+                return;
+        }
+        bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
+        bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
+        page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
+        spin_lock_bh(&mm->context.list_lock);
+        /* Delayed freeing with rcu prevents reuse of pgtable fragments */
+        list_del_init(&page->lru);
+        spin_unlock_bh(&mm->context.list_lock);
+        table = (unsigned long *)(((unsigned long) table) | bits);
+        batch->table[batch->pgt_index++] = table;
+        if (batch->pgt_index >= batch->crst_index)
+                rcu_table_freelist_finish();
+}
+
 void disable_noexec(struct mm_struct *mm, struct task_struct *tsk)
 {
         struct page *page;
 
-        spin_lock(&mm->context.list_lock);
+        spin_lock_bh(&mm->context.list_lock);
         /* Free shadow region and segment tables. */
         list_for_each_entry(page, &mm->context.crst_list, lru)
                 if (page->index) {
@@ -255,7 +392,7 @@ void disable_noexec(struct mm_struct *mm, struct task_struct *tsk)
         /* "Free" second halves of page tables. */
         list_for_each_entry(page, &mm->context.pgtable_list, lru)
                 page->flags &= ~SECOND_HALVES;
-        spin_unlock(&mm->context.list_lock);
+        spin_unlock_bh(&mm->context.list_lock);
         mm->context.noexec = 0;
         update_mm(mm, tsk);
 }