[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>

1 files changed, 154 insertions, 17 deletions

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);
 }