Re: [Qemu-devel] [RFC PATCH 5/7] target-arm: Enable KVM_ARM_VCPU_PSCI_0_2 feature when possible

[Peter Maydell]

[another resend for qemu-devel...]

On 27 February 2014 07:16, Pranavkumar Sawargaonkar
<address@hidden> wrote:
> On 27 February 2014 12:21, Pranavkumar Sawargaonkar
> <address@hidden> wrote:
>> Latest linux kernel supports in-kernel emulation of PSCI v0.2 but
>> to enable it we need to select KVM_ARM_VCPU_PSCI_0_2 feature using
>> KVM_ARM_VCPU_INIT ioctl.
>>
>> Also, we can use KVM_ARM_VCPU_PSCI_0_2 feature for VCPU only when
>> linux kernel has KVM_CAP_ARM_PSCI_0_2 capability.
>>
>> This patch updates kvm_arch_init_vcpu() to enable KVM_ARM_VCPU_PSCI_0_2
>> feature for VCPU when KVM ARM/ARM64 has KVM_CAP_ARM_PSCI_0_2 capability.

I think this has implications for migration. What happens
if you migrate a VM from a host system where the host
kernel supports this capability to one where it doesn't?
(Presumably the answer is "it won't work" and we need
to ensure we don't allow that.)
Conversely, is it OK to migrate a guest from a host
which didn't support PSCI 0.2 to one which does? Does
that work even if the destination has PSCI 0.2 enabled
for the vCPUs, or do we need to support starting a
VM with 0.2 disabled even on 0.2-capable hosts, for
use as a migration target?

Also we still don't seem to have done anything about
migration of the PSCI CPU powerup/down state.

thanks
-- PMM