xen: introduce helper functions to do safe read and write accesses

[cascardo/linux.git] / arch / x86 / include / asm / xen / page.h

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index b54a3d2..5eea099 100644 (file)
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -59,6 +59,20 @@ extern int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
                                     struct page **pages, unsigned int count);
 extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
 
+/*
+ * Helper functions to write or read unsigned long values to/from
+ * memory, when the access may fault.
+ */
+static inline int xen_safe_write_ulong(unsigned long *addr, unsigned long val)
+{
+       return __put_user(val, (unsigned long __user *)addr);
+}
+
+static inline int xen_safe_read_ulong(unsigned long *addr, unsigned long *val)
+{
+       return __get_user(*val, (unsigned long __user *)addr);
+}
+
 /*
  * When to use pfn_to_mfn(), __pfn_to_mfn() or get_phys_to_machine():
  * - pfn_to_mfn() returns either INVALID_P2M_ENTRY or the mfn. No indicator
@@ -125,7 +139,7 @@ static inline unsigned long mfn_to_pfn_no_overrides(unsigned long mfn)
         * In such cases it doesn't matter what we return (we return garbage),
         * but we must handle the fault without crashing!
         */
-       ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
+       ret = xen_safe_read_ulong(&machine_to_phys_mapping[mfn], &pfn);
        if (ret < 0)
                return ~0;