RE: [PATCH RFC V2 17/37] arm/virt/acpi: Build CPUs AML with CPU Hotplug support

[Salil Mehta]

> 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;
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> rafael@kernel.org; borntraeger@linux.ibm.com; alex.bennee@linaro.org;
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> zhukeqian <zhukeqian1@huawei.com>; wangxiongfeng (C)
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> 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.