1 files changed, 49 insertions, 40 deletions

diff --git a/arch/x86/mm/pageattr_32.c b/arch/x86/mm/pageattr_32.c
index 1011b21f8db0..14c923b3b07f 100644
--- a/arch/x86/mm/pageattr_32.c
+++ b/arch/x86/mm/pageattr_32.c
@@ -37,33 +37,6 @@ pte_t *lookup_address(unsigned long address, int *level)
         return pte_offset_kernel(pmd, address);
 }
 
-static struct page *
-split_large_page(unsigned long address, pgprot_t ref_prot)
-{
-        unsigned long addr;
-        struct page *base;
-        pte_t *pbase;
-        int i;
-
-        base = alloc_pages(GFP_KERNEL, 0);
-        if (!base)
-                return NULL;
-
-        /*
-         * page_private is used to track the number of entries in
-         * the page table page that have non standard attributes.
-         */
-        address = __pa(address);
-        addr = address & LARGE_PAGE_MASK;
-        pbase = (pte_t *)page_address(base);
-        paravirt_alloc_pt(&init_mm, page_to_pfn(base));
-
-        for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE)
-                set_pte(&pbase[i], pfn_pte(addr >> PAGE_SHIFT, ref_prot));
-
-        return base;
-}
-
 static void set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
 {
         unsigned long flags;
@@ -88,14 +61,58 @@ static void set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
         spin_unlock_irqrestore(&pgd_lock, flags);
 }
 
+static int
+split_large_page(pte_t *kpte, unsigned long address, pgprot_t ref_prot)
+{
+        int i, level;
+        unsigned long addr;
+        pte_t *pbase, *tmp;
+        struct page *base;
+
+        base = alloc_pages(GFP_KERNEL, 0);
+        if (!base)
+                return -ENOMEM;
+
+        down_write(&init_mm.mmap_sem);
+        /*
+         * Check for races, another CPU might have split this page
+         * up for us already:
+         */
+        tmp = lookup_address(address, &level);
+        if (tmp != kpte)
+                goto out_unlock;
+
+        address = __pa(address);
+        addr = address & LARGE_PAGE_MASK;
+        pbase = (pte_t *)page_address(base);
+        paravirt_alloc_pt(&init_mm, page_to_pfn(base));
+
+        for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE)
+                set_pte(&pbase[i], pfn_pte(addr >> PAGE_SHIFT, ref_prot));
+
+        /*
+         * Install the new, split up pagetable:
+         */
+        set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
+        base = NULL;
+
+out_unlock:
+        up_write(&init_mm.mmap_sem);
+
+        if (base)
+                __free_pages(base, 0);
+
+        return 0;
+}
+
 static int __change_page_attr(struct page *page, pgprot_t prot)
 {
         pgprot_t ref_prot = PAGE_KERNEL;
         struct page *kpte_page;
         unsigned long address;
+        int level, err = 0;
         pgprot_t oldprot;
         pte_t *kpte;
-        int level;
 
         BUG_ON(PageHighMem(page));
         address = (unsigned long)page_address(page);
@@ -127,19 +144,11 @@ repeat:
         if (level == 3) {
                 set_pte_atomic(kpte, mk_pte(page, prot));
         } else {
-                struct page *split;
-
-                split = split_large_page(address, ref_prot);
-                if (!split)
-                        return -ENOMEM;
-
-                /*
-                 * There's a small window here to waste a bit of RAM:
-                 */
-                set_pmd_pte(kpte, address, mk_pte(split, ref_prot));
-                goto repeat;
+                err = split_large_page(kpte, address, ref_prot);
+                if (!err)
+                        goto repeat;
         }
-        return 0;
+        return err;
 }
 
 /*