1 files changed, 57 insertions, 8 deletions

diff --git a/mm/highmem.c b/mm/highmem.c
index b36b83b920ff..910198037bf5 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -67,6 +67,25 @@ pte_t * pkmap_page_table;
 
 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
 
+/*
+ * Most architectures have no use for kmap_high_get(), so let's abstract
+ * the disabling of IRQ out of the locking in that case to save on a
+ * potential useless overhead.
+ */
+#ifdef ARCH_NEEDS_KMAP_HIGH_GET
+#define lock_kmap()             spin_lock_irq(&kmap_lock)
+#define unlock_kmap()           spin_unlock_irq(&kmap_lock)
+#define lock_kmap_any(flags)    spin_lock_irqsave(&kmap_lock, flags)
+#define unlock_kmap_any(flags)  spin_unlock_irqrestore(&kmap_lock, flags)
+#else
+#define lock_kmap()             spin_lock(&kmap_lock)
+#define unlock_kmap()           spin_unlock(&kmap_lock)
+#define lock_kmap_any(flags)    \
+                do { spin_lock(&kmap_lock); (void)(flags); } while (0)
+#define unlock_kmap_any(flags)  \
+                do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
+#endif
+
 static void flush_all_zero_pkmaps(void)
 {
         int i;
@@ -113,9 +132,9 @@ static void flush_all_zero_pkmaps(void)
  */
 void kmap_flush_unused(void)
 {
-        spin_lock(&kmap_lock);
+        lock_kmap();
         flush_all_zero_pkmaps();
-        spin_unlock(&kmap_lock);
+        unlock_kmap();
 }
 
 static inline unsigned long map_new_virtual(struct page *page)
@@ -145,10 +164,10 @@ start:
 
                         __set_current_state(TASK_UNINTERRUPTIBLE);
                         add_wait_queue(&pkmap_map_wait, &wait);
-                        spin_unlock(&kmap_lock);
+                        unlock_kmap();
                         schedule();
                         remove_wait_queue(&pkmap_map_wait, &wait);
-                        spin_lock(&kmap_lock);
+                        lock_kmap();
 
                         /* Somebody else might have mapped it while we slept */
                         if (page_address(page))
@@ -184,29 +203,59 @@ void *kmap_high(struct page *page)
          * For highmem pages, we can't trust "virtual" until
          * after we have the lock.
          */
-        spin_lock(&kmap_lock);
+        lock_kmap();
         vaddr = (unsigned long)page_address(page);
         if (!vaddr)
                 vaddr = map_new_virtual(page);
         pkmap_count[PKMAP_NR(vaddr)]++;
         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
-        spin_unlock(&kmap_lock);
+        unlock_kmap();
         return (void*) vaddr;
 }
 
 EXPORT_SYMBOL(kmap_high);
 
+#ifdef ARCH_NEEDS_KMAP_HIGH_GET
+/**
+ * kmap_high_get - pin a highmem page into memory
+ * @page: &struct page to pin
+ *
+ * Returns the page's current virtual memory address, or NULL if no mapping
+ * exists.  When and only when a non null address is returned then a
+ * matching call to kunmap_high() is necessary.
+ *
+ * This can be called from any context.
+ */
+void *kmap_high_get(struct page *page)
+{
+        unsigned long vaddr, flags;
+
+        lock_kmap_any(flags);
+        vaddr = (unsigned long)page_address(page);
+        if (vaddr) {
+                BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
+                pkmap_count[PKMAP_NR(vaddr)]++;
+        }
+        unlock_kmap_any(flags);
+        return (void*) vaddr;
+}
+#endif
+
 /**
  * kunmap_high - map a highmem page into memory
  * @page: &struct page to unmap
+ *
+ * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
+ * only from user context.
  */
 void kunmap_high(struct page *page)
 {
         unsigned long vaddr;
         unsigned long nr;
+        unsigned long flags;
         int need_wakeup;
 
-        spin_lock(&kmap_lock);
+        lock_kmap_any(flags);
         vaddr = (unsigned long)page_address(page);
         BUG_ON(!vaddr);
         nr = PKMAP_NR(vaddr);
@@ -232,7 +281,7 @@ void kunmap_high(struct page *page)
                  */
                 need_wakeup = waitqueue_active(&pkmap_map_wait);
         }
-        spin_unlock(&kmap_lock);
+        unlock_kmap_any(flags);
 
         /* do wake-up, if needed, race-free outside of the spin lock */
         if (need_wakeup)