Re: [PATCH v2 04/15] KVM: s390: CPU model support for AP virtualization

[Tony Krowiak]

On 02/28/2018 06:58 AM, David Hildenbrand wrote:
> On 28.02.2018 12:40, Christian Borntraeger wrote:
> > On 02/28/2018 10:48 AM, David Hildenbrand wrote:
> > > On 27.02.2018 15:28, Tony Krowiak wrote:
> > > > Introduces a new CPU model feature and two CPU model
> > > > facilities to support AP virtualization for KVM guests.
> > > >
> > > > CPU model feature:
> > > >
> > > > The KVM_S390_VM_CPU_FEAT_AP feature indicates that the
> > > > AP facilities are installed on the KVM guest. This
> > > > feature will be enabled by the kernel only if the AP
> > > > facilities are installed on the linux host. This feature
> > > > must be specifically turned on for the KVM guest from
> > > > userspace to allow guest access to AP devices installed
> > > > on the linux host.
> > > >
> > > > CPU model facilities:
> > > >
> > > > 1. AP Query Configuration Information (QCI) facility is installed.
> > > >
> > > >     This is indicated by setting facilities bit 12 for
> > > >     the guest. The kernel will not enable this facility
> > > >     for the guest if it is not set on the host. This facility
> > > >     must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
> > > >     feature is not installed.
> > > >
> > > > 2. AP Facilities Test facility (APFT) is installed.
> > > >
> > > >     This is indicated by setting facilities bit 15 for
> > > >     the guest. The kernel will not enable this facility for
> > > >     the guest if it is not set on the host. This facility
> > > >     must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
> > > >     feature is not installed.
> > > >
> > > > Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > > > Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >   arch/s390/include/uapi/asm/kvm.h |    1 +
> > > >   arch/s390/kvm/kvm-s390.c         |    4 ++++
> > > >   arch/s390/tools/gen_facilities.c |    2 ++
> > > >   3 files changed, 7 insertions(+), 0 deletions(-)
> > > >
> > > > diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
> > > > index 4cdaa55..a580dec 100644
> > > > --- a/arch/s390/include/uapi/asm/kvm.h
> > > > +++ b/arch/s390/include/uapi/asm/kvm.h
> > > > @@ -130,6 +130,7 @@ struct kvm_s390_vm_cpu_machine {
> > > >   #define KVM_S390_VM_CPU_FEAT_PFMFI	11
> > > >   #define KVM_S390_VM_CPU_FEAT_SIGPIF	12
> > > >   #define KVM_S390_VM_CPU_FEAT_KSS	13
> > > > +#define KVM_S390_VM_CPU_FEAT_AP		14
> > > >   struct kvm_s390_vm_cpu_feat {
> > > >   	__u64 feat[16];
> > > >   };
> > > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > > > index de1e299..c68ca86 100644
> > > > --- a/arch/s390/kvm/kvm-s390.c
> > > > +++ b/arch/s390/kvm/kvm-s390.c
> > > > @@ -347,6 +347,10 @@ static void kvm_s390_cpu_feat_init(void)
> > > >   
> > > >   	if (MACHINE_HAS_ESOP)
> > > >   		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP);
> > > > +
> > > > +	if (ap_instructions_installed()) /* AP instructions installed on host */
> > > > +		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP);
> > > Don't we have a SIE specific AP feature? So is it true, that once we
> > > have AP instructions, we are allowed to use them for SIE? Isn't there a
> > > "AP interpretation facility" or anything like that? (that unlocks ECA_APIE)
> > This seems to be coupled to the AP facility and there is no facility or scp bit.
> > AP is too old to have that (predates STFLE)
> Interesting, so we (I :) ) didn't implement vSIE support back then
> because we never indicated the AP facility (sensed by executing the
> instruction) to the guest.
>
> So ECA_APIE can be used when we sense the AP facility. Thanks!
All true.
>