Re: [Qemu-devel] [PATCH 0/3] arm/virt: refine virt.c code and implement hot_add_cpu interface

[Li Zhang <zhlcindy@gmail.com>]

> 在 2017年5月29日，下午6:43，Igor Mammedov <imammedo@redhat.com> 写道：
> 
> On Sat, 27 May 2017 10:32:33 +0800
> Li Zhang <zhlcindy@gmail.com> wrote:
> 
>>> On Fri, May 26, 2017 at 7:21 PM, Igor Mammedov <imammedo@redhat.com> wrote:
>>> On Fri, 26 May 2017 17:21:05 +0800
>>> Li Zhang <zhlcindy@gmail.com> wrote:
>>> 
>>>> From: Li Zhang <li.zhang@hxt-semitech.com>
>>>> 
>>>> virt machine doesn't support hot_add_cpu interface. This patchset is to implement
>>>> hot_add_cpu interface. A CPU can be added by QMP command with QEMU monitor.
>>>> 
>>>> Here is command to add a CPU with QMP command.
>>>> 
>>>> * qemu-system-aarch64 -machine virt -cpu cortex-a15 -smp 1,maxcpus=4 \
>>>>    -monitor telnet:127.0.0.1:4444,server,nowait -nographic
>>>> * connect monitor:      telnet 127.0.0.1 4444
>>>> * execute qmp command:  cpu-add 1  
>>> cpu-add command shouldn't be used for new cpu hotplug,
>>> pls use generic device_add for that.  
>> 
>> Ok,  I will drop this command and look at device_add.
>> 
>>> 
>>> The last time I looked at it, virt machine needed quite a bit of
>>> re-factoring of the way it creates/wires up CPUs.  
>> 
>> Yes, I am looking into it and see if I can do something:)
>> 
>>> 
>>> Pls see usage of following callbacks for example on how to implement
>>> device_add based cpu hotplug:
>>> 
>>>  get_hotplug_handler
>>>  pc_cpu_pre_plug
>>>  pc_cpu_plug
>>>  pc_possible_cpu_arch_ids
>>> 
>>> and pc_cpus_init() for initial cpu creation with above callbacks in use
>>> 
>> Thanks, I will see it. :)
>> 
>>>> 
>>>> Currently, when KVM is enabled and add a CPU with QMP command, QEMU
>>>> reports error "kvm_init_vcpu failed: Device or resourc busy". KVM can't
>>>> create a new CPU when vgic has been initialized and irqchip_in_kernel in
>>>> function kvm_arch_vcpu_create. It needs to change KVM code in the future.  
>>> if KVM isn't capable do it yet, then qemu should refuse cpu hotplug if running
>>> with KVM accelarator and allow it only in TCG mode.  
>> 
>> OK, I will add an assertion to allow hotplug only in TCG mode.
> instead of assert which will crash guest on hotplug,
> just disable hotplug gracefully (for example set error in pre_plug handler)

OK, got it.

> 
>> 
>>> 
>>>> 
>>>> Li Zhang (3):
>>>>  arm/virt: Refine fdt_add_cpu_nodes code
>>>>  arm/virt: Refine code of machvirt_init
>>>>  arm/virt: Implement hot_add_cpu interface
>>>> 
>>>> hw/arm/virt.c | 344 ++++++++++++++++++++++++++++++++++------------------------
>>>> 1 file changed, 202 insertions(+), 142 deletions(-)
>>>> 
>>> 
>> 
>> 
>> 
>