RE: [PATCH RFC V2 29/37] arm/virt: Update the guest(via GED) about CPU hot-(un)plug events

[Salil Mehta]

Hi Gavin,

> From: Gavin Shan <gshan@redhat.com>
> Sent: Friday, September 29, 2023 1:31 AM
> To: Salil Mehta <salil.mehta@huawei.com>; qemu-devel@nongnu.org; 
> qemu-arm@nongnu.org
> Cc: maz@kernel.org; jean-philippe@linaro.org; Jonathan Cameron
> <jonathan.cameron@huawei.com>; lpieralisi@kernel.org;
> peter.maydell@linaro.org; richard.henderson@linaro.org;
> imammedo@redhat.com; andrew.jones@linux.dev; david@redhat.com;
> philmd@linaro.org; eric.auger@redhat.com; will@kernel.org; ardb@kernel.org;
> oliver.upton@linux.dev; pbonzini@redhat.com; mst@redhat.com;
> rafael@kernel.org; borntraeger@linux.ibm.com; alex.bennee@linaro.org;
> linux@armlinux.org.uk; darren@os.amperecomputing.com;
> ilkka@os.amperecomputing.com; vishnu@os.amperecomputing.com;
> karl.heubaum@oracle.com; miguel.luis@oracle.com; salil.mehta@opnsrc.net;
> zhukeqian <zhukeqian1@huawei.com>; wangxiongfeng (C)
> <wangxiongfeng2@huawei.com>; wangyanan (Y) <wangyanan55@huawei.com>;
> jiakernel2@gmail.com; maobibo@loongson.cn; lixianglai@loongson.cn
> Subject: Re: [PATCH RFC V2 29/37] arm/virt: Update the guest(via GED) about
> CPU hot-(un)plug events
> 
> Hi Salil,
> 
> On 9/26/23 20:04, Salil Mehta wrote:
> > During any vCPU hot-(un)plug, running guest VM needs to be intimated about 
> > the
> > new vCPU being added or request the deletion of the vCPU which is already 
> > part
> > of the guest VM. This is done using the ACPI GED event which eventually gets
> > demultiplexed to a CPU hotplug event and further to specific hot-(un)plug 
> > event
> > of a particular vCPU.
> >
> > This change adds the ACPI calls to the existing hot-(un)plug hooks to 
> > trigger
> > ACPI GED events from QEMU to guest VM.
> >
> > Co-developed-by: Salil Mehta <salil.mehta@huawei.com>
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > ---

[...]

> > @@ -3169,12 +3170,20 @@ static void virt_cpu_plug(HotplugHandler 
> > *hotplug_dev, DeviceState *dev,
> >        * plugged, guest is also notified.
> >        */
> >       if (vms->acpi_dev) {
> > -        /* TODO: update acpi hotplug state. Send cpu hotplug event to 
> > guest */
> > +        HotplugHandlerClass *hhc;
> > +        /* update acpi hotplug state and send cpu hotplug event to guest */
> > +        hhc = HOTPLUG_HANDLER_GET_CLASS(vms->acpi_dev);
> > +        hhc->plug(HOTPLUG_HANDLER(vms->acpi_dev), dev, &local_err);
> > +        if (local_err) {
> > +            goto fail;
> > +        }
> >           /* TODO: register cpu for reset & update F/W info for the next 
> > boot */
> >       }
> >
> >       cs->disabled = false;
> >       return;
> > +fail:
> > +    error_propagate(errp, local_err);
> >   }
> >
> 
> 'fail' tag isn't needed since it's used for once. we can bail early:
> 
>      if (local_err) {
>         error_propagate(errp, local_err);
>         return;
>      }


Agreed. Indeed we can remove goto.


[...]

> > @@ -3202,9 +3213,16 @@ static void virt_cpu_unplug_request(HotplugHandler 
> > *hotplug_dev,
> >           return;
> >       }
> >
> > -    /* TODO: request cpu hotplug from guest */
> > +    /* request cpu hotplug from guest */
> > +    hhc = HOTPLUG_HANDLER_GET_CLASS(vms->acpi_dev);
> > +    hhc->unplug_request(HOTPLUG_HANDLER(vms->acpi_dev), dev, &local_err);
> > +    if (local_err) {
> > +        goto fail;
> > +    }
> >
> >       return;
> > +fail:
> > +    error_propagate(errp, local_err);
> >   }
> >
> 
> Same as above, 'fail' tag isn't needed. Besides, 'return' isn't needed.


Agreed. We can remove goto



[...]

> > @@ -3222,7 +3242,12 @@ static void virt_cpu_unplug(HotplugHandler
> *hotplug_dev, DeviceState *dev,
> >
> >       cpu_slot = virt_find_cpu_slot(ms, cs->cpu_index);
> >
> > -    /* TODO: update the acpi cpu hotplug state for cpu hot-unplug */
> > +    /* update the acpi cpu hotplug state for cpu hot-unplug */
> > +    hhc = HOTPLUG_HANDLER_GET_CLASS(vms->acpi_dev);
> > +    hhc->unplug(HOTPLUG_HANDLER(vms->acpi_dev), dev, &local_err);
> > +    if (local_err) {
> > +        goto fail;
> > +    }
> >
> >       unwire_gic_cpu_irqs(vms, cs);
> >       virt_update_gic(vms, cs);
> > @@ -3236,6 +3261,8 @@ static void virt_cpu_unplug(HotplugHandler
> *hotplug_dev, DeviceState *dev,
> >       cs->disabled = true;
> >
> >       return;
> > +fail:
> > +    error_propagate(errp, local_err);
> >   }
> >
> 
> Same as above.


Agreed. Will fix.


Thanks
Salil.