Re: [PATCH v3] KVM: s390: Add new reset vcpu API

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 8 Jan 2020 15:44:57 +0100
Thomas Huth <thuth@redhat.com> wrote:

> On 08/01/2020 15.38, Christian Borntraeger wrote:
> > 
> > 
> > On 08.01.20 15:35, Janosch Frank wrote:  
> >> On 1/8/20 3:28 PM, Christian Borntraeger wrote:  
> >>>
> >>>
> >>> On 05.12.19 13:09, Janosch Frank wrote:
> >>> [...]  
> >>>> +4.123 KVM_S390_CLEAR_RESET
> >>>> +
> >>>> +Capability: KVM_CAP_S390_VCPU_RESETS
> >>>> +Architectures: s390
> >>>> +Type: vcpu ioctl
> >>>> +Parameters: none
> >>>> +Returns: 0
> >>>> +
> >>>> +This ioctl resets VCPU registers and control structures that QEMU
> >>>> +can't access via the kvm_run structure. The clear reset is a superset
> >>>> +of the initial reset and additionally clears general, access, floating
> >>>> +and vector registers.  
> >>>
> >>> As Thomas outlined, make it more obvious that userspace does the remaining
> >>> parts. I do not think that we want the kernel to do the things (unless it
> >>> helps you in some way for the ultravisor guests)  
> >>
> >> Ok, will do  
> > 
> > I changed my mind (see my other mail) but I would like Thomas, Conny or David
> > to ack/nack.  
> 
> I don't mind too much as long as it is properly documented, but I also
> slightly prefer to be consistent here, i.e. let the kernel clear the
> rest here, too, just like we do it already with the initial reset.

I definitely agree with the 'properly documented' part :) It's probably
enough to just state that the kernel resets the stuff, no need to go
into details (and we also don't need to update this for later versions.)

Q: Are we sure that we will always be able to reset everything from the
kernel?