Re: [RFC PATCH 00/32] ACPI/arm64: add support for virtual cpuhotplug

[Gavin Shan]

Hi Shaoqin,

On 3/29/23 1:52 PM, Shaoqin Huang wrote:
> On 2/3/23 21:50, James Morse wrote:

[...]

> > The first patch has already been posted as a fix here:
> > https://www.spinics.net/lists/linux-ia64/msg21920.html
> > I've only build tested Loongarch and ia64.
> >
> >
> > If folk want to play along at home, you'll need a copy of Qemu that supports this.
> > https://github.com/salil-mehta/qemu.git salil/virt-cpuhp-armv8/rfc-v1-port29092022.psci.present
> >
> > You'll need to fix the numbers of KVM_CAP_ARM_HVC_TO_USER and KVM_CAP_ARM_PSCI_TO_USER
> > to match your host kernel. Replace your '-smp' argument with something like:
> > | -smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
> >
> > then feed the following to the Qemu montior;
> > | (qemu) device_add driver=host-arm-cpu,core-id=1,id=cpu1
> > | (qemu) device_del cpu1
> >
> >
> > This series is based on v6.2-rc3, and can be retrieved from:
> > https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/ virtual_cpu_hotplug/rfc/v1
>
> I applied this patch series on v6.2-rc3 and using the QEMU cloned from the salil-mehta/qemu.git repo. But when I try to run the QEMU, it shows:
>
> $ qemu-system-aarch64: -accel kvm: Failed to enable KVM_CAP_ARM_PSCI_TO_USER cap.
>
> Here is the command I use:
>
> $ qemu-system-aarch64
> -machine virt
> -bios /usr/share/qemu-efi-aarch64/QEMU_EFI.fd
> -accel kvm
> -m 4096
> -smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
> -cpu host
> -qmp unix:./src.socket,server,nowait
> -hda ./XXX.qcow2
> -serial unix:./src.serial,server,nowait
> -monitor stdio
>
> It seems something related to your notice: You'll need to fix the numbers of KVM_CAP_ARM_HVC_TO_USER and KVM_CAP_ARM_PSCI_TO_USER
> to match your host kernel.
>
> But I'm not actually understand what should I fix, since I haven't review the patch series. Could you give me some more information? Maybe I'm doing something wrong.

When the kernel is rebased to v6.2.rc3, the two capabilities are conflictsing
between QEMU and host kernel. Please adjust them like below and have a try:

In qemu/linux-headers/linux/kvm.h

#define KVM_CAP_ARM_HVC_TO_USER 250 /* TODO: as per linux 6.1-rc2 */
#define KVM_CAP_ARM_PSCI_TO_USER 251 /* TODO: as per linux 6.1-rc2 */

In linux/include/uapi/linux/kvm.h

#define KVM_CAP_ARM_HVC_TO_USER 250
#define KVM_CAP_ARM_PSCI_TO_USER 251

Thanks,
Gavin