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

[Bin Meng]

On Tue, Oct 12, 2021 at 9:46 AM MingWang Li <limingwang@huawei.com> wrote:
>
> 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

I see your command line parameters already contain "-object
memory-backend-file share=on", so this error message is not accurate.
Should this message be altered to mention things like what this patch
does?

> 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

typo: because

> 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.
>

How about changing the commit title to: "Use machine->ram as the
system memory" ??

> 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);
>

Regards,
Bin