[PATCH v2] hw/riscv: virt: bugfix the memory-backend-file command is invalid

[MingWang Li]

From: Mingwang Li <limingwang@huawei.com>

When I start the VM with the following command:
$ ./qemu-system-riscv64 -M virt,accel=kvm -m 4096M -cpu host -nographic \
    -name guest=riscv-guset \
    -smp 2 \
    -bios none \
    -kernel ./Image \
    -drive file=./guest.img,format=raw,id=hd0 \
    -device virtio-blk-device,drive=hd0 \
    -append "root=/dev/vda rw console=ttyS0 earlycon=sbi" \
    -object 
memory-backend-file,id=mem,size=4096M,mem-path=/dev/hugepages,share=on \
    -numa node,memdev=mem -mem-prealloc \
    -chardev socket,id=char0,path=/mnt/vhost-net0 \
    -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
    -device 
virtio-net-pci,mac=52:54:00:00:00:01,netdev=mynet1,mrg_rxbuf=on,csum=on,guest_csum=on,guest_ecn=on
 \

Then, QEMU displays the following error information:
qemu-system-riscv64: Failed initializing vhost-user memory map, consider using 
-object memory-backend-file share=on
qemu-system-riscv64: vhost_set_mem_table failed: Interrupted system call (4)
qemu-system-riscv64: unable to start vhost net: 4: falling back on userspace 
virtio

Note that, before starting the kvm-acceled QEMU VM, following
temporarily unaccepted QEMU patches should be used:
https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg02516.html

This error was made bacause default main_mem is used to be registered
as the system memory, other memory cannot be initialized. Therefore,
the system memory should be initialized to the machine->ram, which
consists of the default main_mem and other possible memory required
by applications, such as shared hugepage memory in DPDK.
Also, the mc->defaul_ram_id should be set to the default main_mem,
such as "riscv_virt_board.ram" for the virt machine.

Signed-off-by: Mingwang Li <limingwang@huawei.com>
Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
---
 hw/riscv/virt.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index ec0cb69b8c..b3b431c847 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -771,7 +771,6 @@ static void virt_machine_init(MachineState *machine)
     const MemMapEntry *memmap = virt_memmap;
     RISCVVirtState *s = RISCV_VIRT_MACHINE(machine);
     MemoryRegion *system_memory = get_system_memory();
-    MemoryRegion *main_mem = g_new(MemoryRegion, 1);
     MemoryRegion *mask_rom = g_new(MemoryRegion, 1);
     char *plic_hart_config, *soc_name;
     target_ulong start_addr = memmap[VIRT_DRAM].base;
@@ -890,10 +889,8 @@ static void virt_machine_init(MachineState *machine)
     }
 
     /* register system main memory (actual RAM) */
-    memory_region_init_ram(main_mem, NULL, "riscv_virt_board.ram",
-                           machine->ram_size, &error_fatal);
     memory_region_add_subregion(system_memory, memmap[VIRT_DRAM].base,
-        main_mem);
+        machine->ram);
 
     /* create device tree */
     create_fdt(s, memmap, machine->ram_size, machine->kernel_cmdline,
@@ -1032,6 +1029,7 @@ static void virt_machine_class_init(ObjectClass *oc, void 
*data)
     mc->cpu_index_to_instance_props = riscv_numa_cpu_index_to_props;
     mc->get_default_cpu_node_id = riscv_numa_get_default_cpu_node_id;
     mc->numa_mem_supported = true;
+    mc->default_ram_id = "riscv_virt_board.ram";
 
     machine_class_allow_dynamic_sysbus_dev(mc, TYPE_RAMFB_DEVICE);
 
-- 
2.19.1