RE: [PATCH RFC V2 15/37] arm/virt: Create GED dev before *disabled* CPU Objs are destroyed

[Salil Mehta]

> From: Gavin Shan <gshan@redhat.com>
> Sent: Thursday, September 28, 2023 2:08 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 15/37] arm/virt: Create GED dev before
> *disabled* CPU Objs are destroyed
> 
> Hi Salil,
> 
> On 9/26/23 20:04, Salil Mehta wrote:
> > ACPI CPU hotplug state (is_present=_STA.PRESENT, is_enabled=_STA.ENABLED) 
> > for
> > all the possible vCPUs MUST be initialized during machine init. This is done
> > during the creation of the GED device. VMM/Qemu MUST expose/fake the ACPI 
> > state
> > of the disabled vCPUs to the Guest kernel as 'present' (_STA.PRESENT) always
> > i.e. ACPI persistent. if the 'disabled' vCPU objectes are destroyed before 
> > the
> > GED device has been created then their ACPI hotplug state might not get
> > initialized correctly as acpi_persistent flag is part of the CPUState. This 
> > will
> > expose wrong status of the unplugged vCPUs to the Guest kernel.
> >
> > Hence, moving the GED device creation before disabled vCPU objects get 
> > destroyed
> > as part of the post CPU init routine.
> >
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > ---
> >   hw/arm/virt.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 5c8a0672dc..cbb6199ec6 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -2376,6 +2376,12 @@ static void machvirt_init(MachineState *machine)
> >
> >       create_gic(vms, sysmem);
> >
> > +    has_ged = has_ged && aarch64 && firmware_loaded &&
> > +              virt_is_acpi_enabled(vms);
> > +    if (has_ged) {
> > +        vms->acpi_dev = create_acpi_ged(vms);
> > +    }
> > +
> 
> I prefer the old style. Squeezing all conditions to @has_ged changes what's
> to be meant by @has_ged itself.

The check is too long and a similar piece of code has to used again
down below. Hence, to reuse the result, it's better to store the first
result in a variable.

I can see you point though. To mitigate that I can use a new variable
for this?


Thanks
Salil.


> 
>         if (has_ged && aarch64 && firmware_loaded &&
> virt_is_acpi_enabled(vms)) {
>             :
>         }
> 
> >       virt_cpu_post_init(vms, sysmem);
> >
> >       fdt_add_pmu_nodes(vms);
> > @@ -2398,9 +2404,7 @@ static void machvirt_init(MachineState *machine)
> >
> >       create_pcie(vms);
> >
> > -    if (has_ged && aarch64 && firmware_loaded &&
> virt_is_acpi_enabled(vms)) {
> > -        vms->acpi_dev = create_acpi_ged(vms);
> > -    } else {
> > +    if (!has_ged) {
> >           create_gpio_devices(vms, VIRT_GPIO, sysmem);
> >       }
> >
> 
> Thanks,
> Gavin