Re: [PATCH/RFC] KVM: track pid for VCPU only on KVM_RUN ioctl

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 19/08/14 12:03, Paolo Bonzini wrote:
> Il 19/08/2014 11:59, Christian Borntraeger ha scritto:
>> Its only for the interrupts that are cpu local (like pending IPIs).
>> In addition, we would do that only for the reset case (with an
>> interface that can be used for migration). Right now
>> KVM_S390_INITIAL_RESET takes the vcpu_mutex, so this protects against
>> KVM_RUN.
> 
> I'm not sure, this does seem like a workaround for another limitation
> after all...  Gleb?

Yes. We want to get rid of KVM_S390_INITIAL_RESET in QEMU. This comes from a time, when we had another userspace prototype for KVM on s390 (kuli). Its really a wart that has to go.
Its just that we are not there yet to remove the call to KVM_S390_INITIAL_RESET. Doing so can result in hard to debug errors after reboot, if an interrupt was made pending just before reboot that gets delivered in the new instance.

The new way for local interrupt read/write will probably be some onereg or syncreg interface with a bitmask register and payload registers. We have to solve some concurrency and implemenation issues here.

Christian