hw/i386: add a separate region that tracks the SMRAME bit

This region is exported at /machine/smram.  It is "empty" if
SMRAME=0 and points to SMRAM if SMRAME=1.  The CPU will
enable/disable it as it enters or exits SMRAM.

While touching nearby code, the existing memory region setup was
slightly inconsistent.  The smram_region is *disabled* in order to open
SMRAM (because the smram_region shows the low VRAM instead of the RAM
at 0xa0000).  Because SMRAM is closed at startup, the smram_region must
be enabled when creating the i440fx or q35 devices.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/pci-host/piix.c

@@ -105,6 +105,7 @@ struct PCII440FXState {
     MemoryRegion *ram_memory;
     PAMMemoryRegion pam_regions[13];
     MemoryRegion smram_region;
+    MemoryRegion smram, low_smram;
     uint8_t smm_enabled;
 };
 
@@ -139,6 +140,8 @@ static void i440fx_update_memory_mappings(PCII440FXState *d)
                    pd->config[I440FX_PAM + ((i + 1) / 2)]);
     }
     smram_update(&d->smram_region, pd->config[I440FX_SMRAM], d->smm_enabled);
+    memory_region_set_enabled(&d->smram,
+                              pd->config[I440FX_SMRAM] & SMRAM_G_SMRAME);
     memory_region_transaction_commit();
 }
 
@@ -346,11 +349,23 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state,
     pc_pci_as_mapping_init(OBJECT(f), f->system_memory,
                            f->pci_address_space);
 
+    /* if *disabled* show SMRAM to all CPUs */
     memory_region_init_alias(&f->smram_region, OBJECT(d), "smram-region",
                              f->pci_address_space, 0xa0000, 0x20000);
     memory_region_add_subregion_overlap(f->system_memory, 0xa0000,
                                         &f->smram_region, 1);
-    memory_region_set_enabled(&f->smram_region, false);
+    memory_region_set_enabled(&f->smram_region, true);
+
+    /* smram, as seen by SMM CPUs */
+    memory_region_init(&f->smram, OBJECT(d), "smram", 1ull << 32);
+    memory_region_set_enabled(&f->smram, true);
+    memory_region_init_alias(&f->low_smram, OBJECT(d), "smram-low",
+                             f->system_memory, 0xa0000, 0x20000);
+    memory_region_set_enabled(&f->low_smram, true);
+    memory_region_add_subregion(&f->smram, 0xa0000, &f->low_smram);
+    object_property_add_const_link(qdev_get_machine(), "smram",
+                                   OBJECT(&f->smram), &error_abort);
+
     init_pam(dev, f->ram_memory, f->system_memory, f->pci_address_space,
              &f->pam_regions[0], PAM_BIOS_BASE, PAM_BIOS_SIZE);
     for (i = 0; i < 12; ++i) {

hw/pci-host/q35.c

@@ -270,6 +270,8 @@ static void mch_update_smram(MCHPCIState *mch)
     memory_region_transaction_begin();
     smram_update(&mch->smram_region, pd->config[MCH_HOST_BRIDGE_SMRAM],
                     mch->smm_enabled);
+    memory_region_set_enabled(&mch->smram,
+                              pd->config[MCH_HOST_BRIDGE_SMRAM] & SMRAM_G_SMRAME);
     memory_region_transaction_commit();
 }
 
@@ -399,13 +401,24 @@ static void mch_realize(PCIDevice *d, Error **errp)
     pc_pci_as_mapping_init(OBJECT(mch), mch->system_memory,
                            mch->pci_address_space);
 
-    /* smram */
+    /* if *disabled* show SMRAM to all CPUs */
     cpu_smm_register(&mch_set_smm, mch);
     memory_region_init_alias(&mch->smram_region, OBJECT(mch), "smram-region",
                              mch->pci_address_space, 0xa0000, 0x20000);
     memory_region_add_subregion_overlap(mch->system_memory, 0xa0000,
                                         &mch->smram_region, 1);
-    memory_region_set_enabled(&mch->smram_region, false);
+    memory_region_set_enabled(&mch->smram_region, true);
+
+    /* smram, as seen by SMM CPUs */
+    memory_region_init(&mch->smram, OBJECT(mch), "smram", 1ull << 32);
+    memory_region_set_enabled(&mch->smram, true);
+    memory_region_init_alias(&mch->low_smram, OBJECT(mch), "smram-low",
+                             mch->system_memory, 0xa0000, 0x20000);
+    memory_region_set_enabled(&mch->low_smram, true);
+    memory_region_add_subregion(&mch->smram, 0xa0000, &mch->low_smram);
+    object_property_add_const_link(qdev_get_machine(), "smram",
+                                   OBJECT(&mch->smram), &error_abort);
+
     init_pam(DEVICE(mch), mch->ram_memory, mch->system_memory,
              mch->pci_address_space, &mch->pam_regions[0],
              PAM_BIOS_BASE, PAM_BIOS_SIZE);

include/hw/pci-host/q35.h

@@ -53,6 +53,7 @@ typedef struct MCHPCIState {
     MemoryRegion *address_space_io;
     PAMMemoryRegion pam_regions[13];
     MemoryRegion smram_region;
+    MemoryRegion smram, low_smram;
     PcPciInfo pci_info;
     uint8_t smm_enabled;
     ram_addr_t below_4g_mem_size;