diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
index 4e65bdc559..14e5aebee6 100644
--- a/hw/pci-host/q35.c
+++ b/hw/pci-host/q35.c
@@ -355,6 +355,8 @@ static void mch_reset(DeviceState *qdev)
 
     d->config[MCH_HOST_BRIDGE_SMRAM] = MCH_HOST_BRIDGE_SMRAM_DEFAULT;
     d->config[MCH_HOST_BRIDGE_ESMRAMC] = MCH_HOST_BRIDGE_ESMRAMC_DEFAULT;
+    d->wmask[MCH_HOST_BRIDGE_SMRAM] = MCH_HOST_BRIDGE_SMRAM_WMASK;
+    d->wmask[MCH_HOST_BRIDGE_ESMRAMC] = MCH_HOST_BRIDGE_ESMRAMC_WMASK;
 
     mch_update(mch);
 }
diff --git a/include/hw/pci-host/q35.h b/include/hw/pci-host/q35.h
index d3c7bbbdfe..01b8492551 100644
--- a/include/hw/pci-host/q35.h
+++ b/include/hw/pci-host/q35.h
@@ -140,6 +140,11 @@ typedef struct Q35PCIHost {
 #define MCH_HOST_BRIDGE_UPPER_SYSTEM_BIOS_END  0x100000
 #define MCH_HOST_BRIDGE_SMRAM_DEFAULT           \
     MCH_HOST_BRIDGE_SMRAM_C_BASE_SEG
+#define MCH_HOST_BRIDGE_SMRAM_WMASK             \
+    (MCH_HOST_BRIDGE_SMRAM_D_OPEN |             \
+     MCH_HOST_BRIDGE_SMRAM_D_CLS |              \
+     MCH_HOST_BRIDGE_SMRAM_D_LCK |              \
+     MCH_HOST_BRIDGE_SMRAM_G_SMRAME)
 
 #define MCH_HOST_BRIDGE_ESMRAMC                0x9e
 #define MCH_HOST_BRIDGE_ESMRAMC_H_SMRAME       ((uint8_t)(1 << 7))
@@ -156,6 +161,10 @@ typedef struct Q35PCIHost {
     (MCH_HOST_BRIDGE_ESMRAMC_SM_CACHE | \
      MCH_HOST_BRIDGE_ESMRAMC_SM_L1 |    \
      MCH_HOST_BRIDGE_ESMRAMC_SM_L2)
+#define MCH_HOST_BRIDGE_ESMRAMC_WMASK               \
+    (MCH_HOST_BRIDGE_ESMRAMC_H_SMRAME |             \
+     MCH_HOST_BRIDGE_ESMRAMC_TSEG_SZ_MASK |         \
+     MCH_HOST_BRIDGE_ESMRAMC_T_EN)
 
 /* D1:F0 PCIE* port*/
 #define MCH_PCIE_DEV                           1