Support of vCPU Hotplug requires sequence of ACPI handshakes between Qemu and
Guest kernel when a vCPU is plugged or unplugged. Most of the AML code to
support these handshakes already exists. This AML need to be build during VM
init for ARM architecture as well if the GED support exists.

Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 hw/arm/virt-acpi-build.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 6b674231c2..d27df5030e 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -858,7 +858,18 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
      * the RTC ACPI device at all when using UEFI.
      */
     scope = aml_scope("\\_SB");
-    acpi_dsdt_add_cpus(scope, vms);
+    /* if GED is enabled then cpus AML shall be added as part build_cpus_aml */
+    if (vms->acpi_dev) {
+        CPUHotplugFeatures opts = {
+             .acpi_1_compatible = false,
+             .has_legacy_cphp = false
+        };
+
+        build_cpus_aml(scope, ms, opts, memmap[VIRT_CPUHP_ACPI].base,
+                       "\\_SB", NULL, AML_SYSTEM_MEMORY);
+    } else {
+        acpi_dsdt_add_cpus(scope, vms);
+    }
     acpi_dsdt_add_uart(scope, &memmap[VIRT_UART],
                        (irqmap[VIRT_UART] + ARM_SPI_BASE));
     if (vmc->acpi_expose_flash) {
-- 
2.34.1

Hi Salil,

On 9/26/23 20:04, Salil Mehta wrote:
> Support of vCPU Hotplug requires sequence of ACPI handshakes between Qemu and
> Guest kernel when a vCPU is plugged or unplugged. Most of the AML code to
> support these handshakes already exists. This AML need to be build during VM
> init for ARM architecture as well if the GED support exists.
> 
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>   hw/arm/virt-acpi-build.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 6b674231c2..d27df5030e 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -858,7 +858,18 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>        * the RTC ACPI device at all when using UEFI.
>        */
>       scope = aml_scope("\\_SB");
> -    acpi_dsdt_add_cpus(scope, vms);
> +    /* if GED is enabled then cpus AML shall be added as part build_cpus_aml */
> +    if (vms->acpi_dev) {
> +        CPUHotplugFeatures opts = {
> +             .acpi_1_compatible = false,
> +             .has_legacy_cphp = false
> +        };
> +
> +        build_cpus_aml(scope, ms, opts, memmap[VIRT_CPUHP_ACPI].base,
> +                       "\\_SB", NULL, AML_SYSTEM_MEMORY);
> +    } else {
> +        acpi_dsdt_add_cpus(scope, vms);
> +    }
>       acpi_dsdt_add_uart(scope, &memmap[VIRT_UART],
>                          (irqmap[VIRT_UART] + ARM_SPI_BASE));
>       if (vmc->acpi_expose_flash) {

I don't think it's enough to check vms->acpi_dev. vCPU hotplug needn't to be
supported even vms->acpi_dev exists. For example when vGICv2 instead of
vGICv3 is enabled, and so on.

Thanks,
Gavin

> From: Gavin Shan <gshan@redhat.com>
> Sent: Thursday, September 28, 2023 2:36 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 17/37] arm/virt/acpi: Build CPUs AML with CPU
> Hotplug support
> 
> Hi Salil,
> 
> On 9/26/23 20:04, Salil Mehta wrote:
> > Support of vCPU Hotplug requires sequence of ACPI handshakes between Qemu
> and
> > Guest kernel when a vCPU is plugged or unplugged. Most of the AML code to
> > support these handshakes already exists. This AML need to be build during VM
> > init for ARM architecture as well if the GED support exists.
> >
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > ---
> >   hw/arm/virt-acpi-build.c | 13 ++++++++++++-
> >   1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> > index 6b674231c2..d27df5030e 100644
> > --- a/hw/arm/virt-acpi-build.c
> > +++ b/hw/arm/virt-acpi-build.c
> > @@ -858,7 +858,18 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> VirtMachineState *vms)
> >        * the RTC ACPI device at all when using UEFI.
> >        */
> >       scope = aml_scope("\\_SB");
> > -    acpi_dsdt_add_cpus(scope, vms);
> > +    /* if GED is enabled then cpus AML shall be added as part build_cpus_aml */
> > +    if (vms->acpi_dev) {
> > +        CPUHotplugFeatures opts = {
> > +             .acpi_1_compatible = false,
> > +             .has_legacy_cphp = false
> > +        };
> > +
> > +        build_cpus_aml(scope, ms, opts, memmap[VIRT_CPUHP_ACPI].base,
> > +                       "\\_SB", NULL, AML_SYSTEM_MEMORY);
> > +    } else {
> > +        acpi_dsdt_add_cpus(scope, vms);
> > +    }
> >       acpi_dsdt_add_uart(scope, &memmap[VIRT_UART],
> >                          (irqmap[VIRT_UART] + ARM_SPI_BASE));
> >       if (vmc->acpi_expose_flash) {
> 
> I don't think it's enough to check vms->acpi_dev. vCPU hotplug needn't to be
> supported even vms->acpi_dev exists. For example when vGICv2 instead of
> vGICv3 is enabled, and so on.

Good catch.

'mc->has_hotpluggable_cpus' has to be added. Will fix.

Thanks
Salil.