diff --git a/xen/arch/x86/include/asm/uaccess.h b/xen/arch/x86/include/asm/uaccess.h
index 2d01669b9610..6b8150ac221a 100644
--- a/xen/arch/x86/include/asm/uaccess.h
+++ b/xen/arch/x86/include/asm/uaccess.h
@@ -24,9 +24,6 @@ unsigned int copy_from_unsafe_ll(void *to, const void *from, unsigned int n);
 void noreturn __get_user_bad(void);
 void noreturn __put_user_bad(void);
 
-#define UA_KEEP(args...) args
-#define UA_DROP(args...)
-
 /**
  * get_guest: - Get a simple variable from guest space.
  * @x:   Variable to store result.
@@ -104,7 +101,7 @@ void noreturn __put_user_bad(void);
 #define put_unsafe(x, ptr)						\
 ({									\
 	int err_; 							\
-	put_unsafe_size(x, ptr, sizeof(*(ptr)), UA_DROP, err_, -EFAULT);\
+	put_unsafe_size(x, ptr, sizeof(*(ptr)), 0, err_, -EFAULT);      \
 	err_;								\
 })
 
@@ -126,7 +123,7 @@ void noreturn __put_user_bad(void);
 #define get_unsafe(x, ptr)						\
 ({									\
 	int err_; 							\
-	get_unsafe_size(x, ptr, sizeof(*(ptr)), UA_DROP, err_, -EFAULT);\
+	get_unsafe_size(x, ptr, sizeof(*(ptr)), 0, err_, -EFAULT);	\
 	err_;								\
 })
 
@@ -155,9 +152,9 @@ struct __large_struct { unsigned long buf[100]; };
  */
 #define put_unsafe_asm(x, addr, GUARD, err, itype, rtype, ltype, errret) \
 	__asm__ __volatile__(						\
-		GUARD(							\
+		".if " STR(GUARD) "\n"					\
 		"	guest_access_mask_ptr %[ptr], %[scr1], %[scr2]\n" \
-		)							\
+		".endif\n"						\
 		"1:	mov"itype" %"rtype"[val], (%[ptr])\n"		\
 		"2:\n"							\
 		".section .fixup,\"ax\"\n"				\
@@ -165,16 +162,16 @@ struct __large_struct { unsigned long buf[100]; };
 		"	jmp 2b\n"					\
 		".previous\n"						\
 		_ASM_EXTABLE(1b, 3b)					\
-		: [ret] "+r" (err), [ptr] "=&r" (dummy_)		\
-		  GUARD(, [scr1] "=&r" (dummy_), [scr2] "=&r" (dummy_))	\
+		: [ret] "+r" (err), [ptr] "=&r" (dummy_),		\
+		  [scr1] "=&r" (dummy_), [scr2] "=&r" (dummy_)		\
 		: [val] ltype (x), "m" (__m(addr)),			\
 		  "[ptr]" (addr), [errno] "i" (errret))
 
 #define get_unsafe_asm(x, addr, GUARD, err, rtype, ltype, errret)	\
 	__asm__ __volatile__(						\
-		GUARD(							\
+		".if " STR(GUARD) "\n"					\
 		"	guest_access_mask_ptr %[ptr], %[scr1], %[scr2]\n" \
-		)							\
+		".endif\n"						\
 		"1:	mov (%[ptr]), %"rtype"[val]\n"			\
 		"2:\n"							\
 		".section .fixup,\"ax\"\n"				\
@@ -184,14 +181,15 @@ struct __large_struct { unsigned long buf[100]; };
 		".previous\n"						\
 		_ASM_EXTABLE(1b, 3b)					\
 		: [ret] "+r" (err), [val] ltype (x),			\
-		  [ptr] "=&r" (dummy_)					\
-		  GUARD(, [scr1] "=&r" (dummy_), [scr2] "=&r" (dummy_))	\
+		  [ptr] "=&r" (dummy_),					\
+		  [scr1] "=&r" (dummy_), [scr2] "=&r" (dummy_)		\
 		: "m" (__m(addr)), "[ptr]" (addr),			\
 		  [errno] "i" (errret))
 
 #define put_unsafe_size(x, ptr, size, grd, retval, errret)                 \
 do {                                                                       \
     retval = 0;                                                            \
+    BUILD_BUG_ON((grd) != 0 && (grd) != 1);                                \
     stac();                                                                \
     switch ( size )                                                        \
     {                                                                      \
@@ -214,11 +212,12 @@ do {                                                                       \
 } while ( false )
 
 #define put_guest_size(x, ptr, size, retval, errret) \
-    put_unsafe_size(x, ptr, size, UA_KEEP, retval, errret)
+    put_unsafe_size(x, ptr, size, 1, retval, errret)
 
 #define get_unsafe_size(x, ptr, size, grd, retval, errret)                 \
 do {                                                                       \
     retval = 0;                                                            \
+    BUILD_BUG_ON((grd) != 0 && (grd) != 1);                                \
     stac();                                                                \
     switch ( size )                                                        \
     {                                                                      \
@@ -233,7 +232,7 @@ do {                                                                       \
 } while ( false )
 
 #define get_guest_size(x, ptr, size, retval, errret)                       \
-    get_unsafe_size(x, ptr, size, UA_KEEP, retval, errret)
+    get_unsafe_size(x, ptr, size, 1, retval, errret)
 
 /**
  * __copy_to_guest_pv: - Copy a block of data into guest space, with less
@@ -333,16 +332,16 @@ copy_to_unsafe(void __user *to, const void *from, unsigned int n)
 
         switch (n) {
         case 1:
-            put_unsafe_size(*(const uint8_t *)from, to, 1, UA_DROP, ret, 1);
+            put_unsafe_size(*(const uint8_t *)from, to, 1, 0, ret, 1);
             return ret;
         case 2:
-            put_unsafe_size(*(const uint16_t *)from, to, 2, UA_DROP, ret, 2);
+            put_unsafe_size(*(const uint16_t *)from, to, 2, 0, ret, 2);
             return ret;
         case 4:
-            put_unsafe_size(*(const uint32_t *)from, to, 4, UA_DROP, ret, 4);
+            put_unsafe_size(*(const uint32_t *)from, to, 4, 0, ret, 4);
             return ret;
         case 8:
-            put_unsafe_size(*(const uint64_t *)from, to, 8, UA_DROP, ret, 8);
+            put_unsafe_size(*(const uint64_t *)from, to, 8, 0, ret, 8);
             return ret;
         }
     }
@@ -374,16 +373,16 @@ copy_from_unsafe(void *to, const void __user *from, unsigned int n)
         switch ( n )
         {
         case 1:
-            get_unsafe_size(*(uint8_t *)to, from, 1, UA_DROP, ret, 1);
+            get_unsafe_size(*(uint8_t *)to, from, 1, 0, ret, 1);
             return ret;
         case 2:
-            get_unsafe_size(*(uint16_t *)to, from, 2, UA_DROP, ret, 2);
+            get_unsafe_size(*(uint16_t *)to, from, 2, 0, ret, 2);
             return ret;
         case 4:
-            get_unsafe_size(*(uint32_t *)to, from, 4, UA_DROP, ret, 4);
+            get_unsafe_size(*(uint32_t *)to, from, 4, 0, ret, 4);
             return ret;
         case 8:
-            get_unsafe_size(*(uint64_t *)to, from, 8, UA_DROP, ret, 8);
+            get_unsafe_size(*(uint64_t *)to, from, 8, 0, ret, 8);
             return ret;
         }
     }
diff --git a/xen/arch/x86/usercopy.c b/xen/arch/x86/usercopy.c
index 7ab2009efe4c..286080f68f7e 100644
--- a/xen/arch/x86/usercopy.c
+++ b/xen/arch/x86/usercopy.c
@@ -11,23 +11,23 @@
 #include <asm/uaccess.h>
 
 #ifndef GUARD
-# define GUARD UA_KEEP
+# define GUARD 1 /* Keep speculative harden guards. */
 #endif
 
 unsigned int copy_to_guest_ll(void __user *to, const void *from, unsigned int n)
 {
-    GUARD(unsigned dummy);
+    unsigned dummy;
 
     stac();
     asm volatile (
-        GUARD(
+        ".if " STR(GUARD) "\n"
         "    guest_access_mask_ptr %[to], %q[scratch1], %q[scratch2]\n"
-        )
+        ".endif\n"
         "1:  rep movsb\n"
         "2:\n"
         _ASM_EXTABLE(1b, 2b)
-        : [cnt] "+c" (n), [to] "+D" (to), [from] "+S" (from)
-          GUARD(, [scratch1] "=&r" (dummy), [scratch2] "=&r" (dummy))
+        : [cnt] "+c" (n), [to] "+D" (to), [from] "+S" (from),
+          [scratch1] "=&r" (dummy), [scratch2] "=&r" (dummy)
         :: "memory" );
     clac();
 
@@ -40,9 +40,9 @@ unsigned int copy_from_guest_ll(void *to, const void __user *from, unsigned int
 
     stac();
     asm volatile (
-        GUARD(
+        ".if " STR(GUARD) "\n"
         "    guest_access_mask_ptr %[from], %q[scratch1], %q[scratch2]\n"
-        )
+        ".endif\n"
         "1:  rep movsb\n"
         "2:\n"
         ".section .fixup,\"ax\"\n"
@@ -56,15 +56,15 @@ unsigned int copy_from_guest_ll(void *to, const void __user *from, unsigned int
         ".previous\n"
         _ASM_EXTABLE(1b, 6b)
         : [cnt] "+c" (n), [to] "+D" (to), [from] "+S" (from),
-          [aux] "=&r" (dummy)
-          GUARD(, [scratch1] "=&r" (dummy), [scratch2] "=&r" (dummy))
+          [aux] "=&r" (dummy),
+          [scratch1] "=&r" (dummy), [scratch2] "=&r" (dummy)
         :: "memory" );
     clac();
 
     return n;
 }
 
-#if GUARD(1) + 0
+#if GUARD
 
 /**
  * copy_to_guest_pv: - Copy a block of data into PV guest space.
@@ -140,14 +140,14 @@ unsigned int copy_from_guest_pv(void *to, const void __user *from,
 }
 
 # undef GUARD
-# define GUARD UA_DROP
+# define GUARD 0 /* Drop speculative harden guards. */
 # define copy_to_guest_ll copy_to_unsafe_ll
 # define copy_from_guest_ll copy_from_unsafe_ll
 # undef __user
 # define __user
 # include __FILE__
 
-#endif /* GUARD(1) */
+#endif /* GUARD */
 
 /*
  * Local variables:
