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

[limingwang (A)]

> >
> > From: Mingwang Li <limingwang@huawei.com>
> >
> > If 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.
> 
> Which command did you use to expose the error? It looks like not every
> machine is done like this patch does.
> 

The command we used to expose the error is as follows:
./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

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

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

If other type of machine is configured when starting a QEMU VM, corresponding 
codes in the machine model should be modified as well.


> Please reword the commit summary a little bit to help the understanding.
> 
> > Also, the mc->defaul_ram_id should be set to the default main_mem,
> > which is named as "riscv_virt_board.ram".
> >
> > Signed-off-by: Mingwang Li <limingwang@huawei.com>
> > Signed-off-by: Yifei Jiang <jiangyifei@huawei.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);
> >
> > --
> 
> Regards,
> Bin