pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS

'etc/reserved-memory-end' will allow QEMU to tell BIOS where PCI
BARs mapping could safely start in high memory.

Allowing BIOS to start mapping 64-bit PCI BARs at address where it
wouldn't conflict with other mappings QEMU might place before it.

That permits QEMU to reserve extra address space before
64-bit PCI hole for memory hotplug.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -1226,7 +1226,8 @@ FWCfgState *pc_memory_init(MemoryRegion *system_memory,
     }
 
     /* initialize hotplug memory address space */
-    if (ram_size < machine->maxram_size) {
+    if (guest_info->has_reserved_memory &&
+        (ram_size < machine->maxram_size)) {
         ram_addr_t hotplug_mem_size =
             machine->maxram_size - ram_size;
 
@@ -1266,6 +1267,12 @@ FWCfgState *pc_memory_init(MemoryRegion *system_memory,
     fw_cfg = bochs_bios_init();
     rom_set_fw(fw_cfg);
 
+    if (guest_info->has_reserved_memory && pcms->hotplug_memory_base) {
+        uint64_t *val = g_malloc(sizeof(*val));
+        *val = cpu_to_le64(ROUND_UP(pcms->hotplug_memory_base, 0x1ULL << 30));
+        fw_cfg_add_file(fw_cfg, "etc/reserved-memory-end", val, sizeof(*val));
+    }
+
     if (linux_boot) {
         load_linux(fw_cfg, kernel_filename, initrd_filename, kernel_cmdline, below_4g_mem_size);
     }

hw/i386/pc_piix.c

@@ -67,6 +67,7 @@ static bool smbios_legacy_mode;
  * pages in the host.
  */
 static bool gigabyte_align = true;
+static bool has_reserved_memory = true;
 
 /* PC hardware initialisation */
 static void pc_init1(MachineState *machine,
@@ -143,6 +144,7 @@ static void pc_init1(MachineState *machine,
 
     guest_info->has_pci_info = has_pci_info;
     guest_info->isapc_ram_fw = !pci_enabled;
+    guest_info->has_reserved_memory = has_reserved_memory;
 
     if (smbios_defaults) {
         MachineClass *mc = MACHINE_GET_CLASS(machine);
@@ -267,6 +269,7 @@ static void pc_init_pci(MachineState *machine)
 static void pc_compat_2_0(MachineState *machine)
 {
     smbios_legacy_mode = true;
+    has_reserved_memory = false;
 }
 
 static void pc_compat_1_7(MachineState *machine)

hw/i386/pc_q35.c

@@ -57,6 +57,7 @@ static bool smbios_legacy_mode;
  * pages in the host.
  */
 static bool gigabyte_align = true;
+static bool has_reserved_memory = true;
 
 /* PC hardware initialisation */
 static void pc_q35_init(MachineState *machine)
@@ -130,6 +131,7 @@ static void pc_q35_init(MachineState *machine)
     guest_info->has_pci_info = has_pci_info;
     guest_info->isapc_ram_fw = false;
     guest_info->has_acpi_build = has_acpi_build;
+    guest_info->has_reserved_memory = has_reserved_memory;
 
     if (smbios_defaults) {
         MachineClass *mc = MACHINE_GET_CLASS(machine);
@@ -245,6 +247,7 @@ static void pc_q35_init(MachineState *machine)
 static void pc_compat_2_0(MachineState *machine)
 {
     smbios_legacy_mode = true;
+    has_reserved_memory = false;
 }
 
 static void pc_compat_1_7(MachineState *machine)

include/hw/i386/pc.h

@@ -77,6 +77,7 @@ struct PcGuestInfo {
     uint64_t *node_cpu;
     FWCfgState *fw_cfg;
     bool has_acpi_build;
+    bool has_reserved_memory;
 };
 
 /* parallel.c */