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

["limingwang (A)" <limingwang@huawei.com>]

On Wed, Oct 13, 2021 at 22:41 PM Bin Meng <bin.meng@windriver.com> wrote:
> 
> 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=o
> > n,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.

QEMU uses this command to alloc fd in the "memory_region_init_ram_from_file" function
and assigns the value of fd to mr->ram_block-fd. If the QEMU uses the default memory to
initialize the system, the QEMU cannot obtain the fd in the "vhost_user_mem_section_filter" 
function when initializing the vhost-user. As a result, an error is reported in the "vhost_user_fill_set_mem_table_msg"
function.

Because of the above bug, even if "-object memory-backend-file share=on" is added to the command line,
the QEMU still reports an error.
This patch can solve this bug.

> Should this message be altered to mention things like what this patch does?

Thanks, I will rewrite the message in next version.
> 
> > 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
> 
Thanks.

> > 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" ??
> 

I think it is just a bugfix.

> > 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