diff --git a/atomic_template.h b/atomic_template.h
index cf83725..b400b2a 100644
--- a/atomic_template.h
+++ b/atomic_template.h
@@ -18,7 +18,11 @@
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */
 
-#if DATA_SIZE == 8
+#if DATA_SIZE == 16
+# define SUFFIX     o
+# define DATA_TYPE  Int128
+# define BSWAP      bswap128
+#elif DATA_SIZE == 8
 # define SUFFIX     q
 # define DATA_TYPE  uint64_t
 # define BSWAP      bswap64
@@ -61,6 +65,21 @@ ABI_TYPE ATOMIC_NAME(cmpxchg)(CPUArchState *env, target_ulong addr,
     return atomic_cmpxchg__nocheck(haddr, cmpv, newv);
 }
 
+#if DATA_SIZE >= 16
+ABI_TYPE ATOMIC_NAME(ld)(CPUArchState *env, target_ulong addr EXTRA_ARGS)
+{
+    DATA_TYPE val, *haddr = ATOMIC_MMU_LOOKUP;
+    __atomic_load(haddr, &val, __ATOMIC_RELAXED);
+    return val;
+}
+
+void ATOMIC_NAME(st)(CPUArchState *env, target_ulong addr,
+                     ABI_TYPE val EXTRA_ARGS)
+{
+    DATA_TYPE *haddr = ATOMIC_MMU_LOOKUP;
+    __atomic_store(haddr, &val, __ATOMIC_RELAXED);
+}
+#else
 ABI_TYPE ATOMIC_NAME(xchg)(CPUArchState *env, target_ulong addr,
                            ABI_TYPE val EXTRA_ARGS)
 {
@@ -86,6 +105,8 @@ GEN_ATOMIC_HELPER(or_fetch)
 GEN_ATOMIC_HELPER(xor_fetch)
 
 #undef GEN_ATOMIC_HELPER
+#endif /* DATA SIZE >= 16 */
+
 #undef END
 
 #if DATA_SIZE > 1
@@ -105,6 +126,22 @@ ABI_TYPE ATOMIC_NAME(cmpxchg)(CPUArchState *env, target_ulong addr,
     return BSWAP(atomic_cmpxchg__nocheck(haddr, BSWAP(cmpv), BSWAP(newv)));
 }
 
+#if DATA_SIZE >= 16
+ABI_TYPE ATOMIC_NAME(ld)(CPUArchState *env, target_ulong addr EXTRA_ARGS)
+{
+    DATA_TYPE val, *haddr = ATOMIC_MMU_LOOKUP;
+    __atomic_load(haddr, &val, __ATOMIC_RELAXED);
+    return BSWAP(val);
+}
+
+void ATOMIC_NAME(st)(CPUArchState *env, target_ulong addr,
+                     ABI_TYPE val EXTRA_ARGS)
+{
+    DATA_TYPE *haddr = ATOMIC_MMU_LOOKUP;
+    val = BSWAP(val);
+    __atomic_store(haddr, &val, __ATOMIC_RELAXED);
+}
+#else
 ABI_TYPE ATOMIC_NAME(xchg)(CPUArchState *env, target_ulong addr,
                            ABI_TYPE val EXTRA_ARGS)
 {
@@ -166,6 +203,7 @@ ABI_TYPE ATOMIC_NAME(add_fetch)(CPUArchState *env, target_ulong addr,
         ldo = ldn;
     }
 }
+#endif /* DATA_SIZE >= 16 */
 
 #undef END
 #endif /* DATA_SIZE > 1 */
diff --git a/configure b/configure
index dd9e679..a499705 100755
--- a/configure
+++ b/configure
@@ -1216,7 +1216,10 @@ case "$cpu" in
            cc_i386='$(CC) -m32'
            ;;
     x86_64)
-           CPU_CFLAGS="-m64"
+           # ??? Only extremely old AMD cpus do not have cmpxchg16b.
+           # If we truly care, we should simply detect this case at
+           # runtime and generate the fallback to serial emulation.
+           CPU_CFLAGS="-m64 -mcx16"
            LDFLAGS="-m64 $LDFLAGS"
            cc_i386='$(CC) -m32'
            ;;
@@ -4491,6 +4494,26 @@ if compile_prog "" "" ; then
     int128=yes
 fi
 
+#########################################
+# See if 128-bit atomic operations are supported.
+
+atomic128=no
+if test "$int128" = "yes"; then
+  cat > $TMPC << EOF
+int main(void)
+{
+  unsigned __int128 x = 0, y = 0;
+  y = __atomic_load_16(&x, 0);
+  __atomic_store_16(&x, y, 0);
+  __atomic_compare_exchange_16(&x, &y, x, 0, 0, 0);
+  return 0;
+}
+EOF
+  if compile_prog "" "" ; then
+    atomic128=yes
+  fi
+fi
+
 ########################################
 # check if getauxval is available.
 
@@ -5447,6 +5470,10 @@ if test "$int128" = "yes" ; then
   echo "CONFIG_INT128=y" >> $config_host_mak
 fi
 
+if test "$atomic128" = "yes" ; then
+  echo "CONFIG_ATOMIC128=y" >> $config_host_mak
+fi
+
 if test "$getauxval" = "yes" ; then
   echo "CONFIG_GETAUXVAL=y" >> $config_host_mak
 fi
diff --git a/cputlb.c b/cputlb.c
index 4f2c500..845b2a7 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -690,6 +690,11 @@ static void *atomic_mmu_lookup(CPUArchState *env, target_ulong addr,
 #define DATA_SIZE 8
 #include "atomic_template.h"
 
+#ifdef CONFIG_ATOMIC128
+#define DATA_SIZE 16
+#include "atomic_template.h"
+#endif
+
 /* Second set of helpers are directly callable from TCG as helpers.  */
 
 #undef EXTRA_ARGS
diff --git a/include/qemu/int128.h b/include/qemu/int128.h
index d4c6e44..5c9890d 100644
--- a/include/qemu/int128.h
+++ b/include/qemu/int128.h
@@ -2,6 +2,7 @@
 #define INT128_H
 
 #ifdef CONFIG_INT128
+#include "qemu/bswap.h"
 
 typedef __int128_t Int128;
 
@@ -137,6 +138,11 @@ static inline void int128_subfrom(Int128 *a, Int128 b)
     *a -= b;
 }
 
+static inline Int128 bswap128(Int128 a)
+{
+    return int128_make128(bswap64(int128_gethi(a)), bswap64(int128_getlo(a)));
+}
+
 #else /* !CONFIG_INT128 */
 
 typedef struct Int128 Int128;
diff --git a/tcg-runtime.c b/tcg-runtime.c
index aa55d12..e952153 100644
--- a/tcg-runtime.c
+++ b/tcg-runtime.c
@@ -133,4 +133,22 @@ static void *atomic_mmu_lookup(CPUArchState *env, target_ulong addr,
 #define DATA_SIZE 8
 #include "atomic_template.h"
 
+/* The following is only callable from other helpers, and matches up
+   with the softmmu version.  */
+
+#ifdef CONFIG_ATOMIC128
+
+#undef EXTRA_ARGS
+#undef ATOMIC_NAME
+#undef ATOMIC_MMU_LOOKUP
+
+#define EXTRA_ARGS     , TCGMemOpIdx oi, uintptr_t retaddr
+#define ATOMIC_NAME(X) \
+    HELPER(glue(glue(glue(atomic_ ## X, SUFFIX), END), _mmu))
+#define ATOMIC_MMU_LOOKUP  atomic_mmu_lookup(env, addr, DATA_SIZE, retaddr)
+
+#define DATA_SIZE 16
+#include "atomic_template.h"
+#endif /* CONFIG_ATOMIC128 */
+
 #endif /* !CONFIG_SOFTMMU */
diff --git a/tcg/tcg.h b/tcg/tcg.h
index 5931965..bc3ea7a 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -1229,7 +1229,29 @@ GEN_ATOMIC_HELPER_ALL(xchg)
 
 #undef GEN_ATOMIC_HELPER_ALL
 #undef GEN_ATOMIC_HELPER
-
 #endif /* CONFIG_SOFTMMU */
 
+#ifdef CONFIG_ATOMIC128
+#include "qemu/int128.h"
+
+/* These aren't really a "proper" helpers because TCG cannot manage Int128.
+   However, use the same format as the others, for use by the backends. */
+Int128 helper_atomic_cmpxchgo_le_mmu(CPUArchState *env, target_ulong addr,
+                                     Int128 cmpv, Int128 newv,
+                                     TCGMemOpIdx oi, uintptr_t retaddr);
+Int128 helper_atomic_cmpxchgo_be_mmu(CPUArchState *env, target_ulong addr,
+                                     Int128 cmpv, Int128 newv,
+                                     TCGMemOpIdx oi, uintptr_t retaddr);
+
+Int128 helper_atomic_ldo_le_mmu(CPUArchState *env, target_ulong addr,
+                                TCGMemOpIdx oi, uintptr_t retaddr);
+Int128 helper_atomic_ldo_be_mmu(CPUArchState *env, target_ulong addr,
+                                TCGMemOpIdx oi, uintptr_t retaddr);
+void helper_atomic_sto_le_mmu(CPUArchState *env, target_ulong addr, Int128 val,
+                              TCGMemOpIdx oi, uintptr_t retaddr);
+void helper_atomic_sto_be_mmu(CPUArchState *env, target_ulong addr, Int128 val,
+                              TCGMemOpIdx oi, uintptr_t retaddr);
+
+#endif /* CONFIG_ATOMIC128 */
+
 #endif /* TCG_H */
