Re: [PATCH 19/32] KVM: s390: mechanism to enable guest zPCI Interpretation

[Matthew Rosato]

On 12/10/21 8:27 AM, Christian Borntraeger wrote:
> Am 07.12.21 um 21:57 schrieb Matthew Rosato:
> > The guest must have access to certain facilities in order to allow
> > interpretive execution of zPCI instructions and adapter event
> > notifications.  However, there are some cases where a guest might
> > disable interpretation -- provide a mechanism via which we can defer
> > enabling the associated zPCI interpretation facilities until the guest
> > indicates it wishes to use them.
> >
> > Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > ---
> >   arch/s390/include/asm/kvm_host.h |  4 +++
> >   arch/s390/kvm/kvm-s390.c         | 43 ++++++++++++++++++++++++++++++++
> >   arch/s390/kvm/kvm-s390.h         | 10 ++++++++
> >   3 files changed, 57 insertions(+)
> >
> > diff --git a/arch/s390/include/asm/kvm_host.h 
> > b/arch/s390/include/asm/kvm_host.h
> > index 3f147b8d050b..38982c1de413 100644
> > --- a/arch/s390/include/asm/kvm_host.h
> > +++ b/arch/s390/include/asm/kvm_host.h
> > @@ -252,7 +252,10 @@ struct kvm_s390_sie_block {
> >   #define ECB2_IEP    0x20
> >   #define ECB2_PFMFI    0x08
> >   #define ECB2_ESCA    0x04
> > +#define ECB2_ZPCI_LSI    0x02
> >       __u8    ecb2;                   /* 0x0062 */
> > +#define ECB3_AISI    0x20
> > +#define ECB3_AISII    0x10
> >   #define ECB3_DEA 0x08
> >   #define ECB3_AES 0x04
> >   #define ECB3_RI  0x01
> > @@ -938,6 +941,7 @@ struct kvm_arch{
> >       int use_cmma;
> >       int use_pfmfi;
> >       int use_skf;
> > +    int use_zpci_interp;
> >       int user_cpu_state_ctrl;
> >       int user_sigp;
> >       int user_stsi;
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index a680f2a02b67..361d742cdf0d 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -1023,6 +1023,47 @@ static int kvm_s390_vm_set_crypto(struct kvm 
> > *kvm, struct kvm_device_attr *attr)
> >       return 0;
> >   }
> > +static void kvm_s390_vcpu_pci_setup(struct kvm_vcpu *vcpu)
> > +{
> > +    /*
> > +     * If the facilities aren't available for PCI interpretation and
> > +     * interrupt forwarding, we shouldn't be here.
> > +     */
>
> This reads like we want a WARN_ON or BUG_ON, but as we call this 
> uncoditionally this is
> actually a valid check. So instead of "shouldn't be here" say something 
> like "bail out
> if interpretion is not active".  ?

Right, this comment block is plain wrong.  We expect to get here under 
multiple circumstances and its OK for this bit to be off:
- initial vcpu setup (use_zpci_interp is off)
- Right after we set use_zpci_interp=1 (turn on ECB for all vcpu)
- hotplug vcpu setup (use_zpci_interp might be on or off)

Will re-word.

> > +    if (!vcpu->kvm->arch.use_zpci_interp)
> > +        return;
> > +
> > +    vcpu->arch.sie_block->ecb2 |= ECB2_ZPCI_LSI;
> > +    vcpu->arch.sie_block->ecb3 |= ECB3_AISII + ECB3_AISI;
> > +}
> > +
> > +void kvm_s390_vcpu_pci_enable_interp(struct kvm *kvm)
> > +{
> > +    struct kvm_vcpu *vcpu;
> > +    int i;
> > +
> > +    /*
> > +     * If host facilities are available, turn on interpretation for the
> > +     * life of this guest
> > +     */
> > +    if (!test_facility(69) || !test_facility(70) || 
> > !test_facility(71) ||
> > +        !test_facility(72))
> > +        return;
>
> Wouldnt that also enable interpretion for VSIE? I guess we should check 
> for the
> sclp facilities from patches 1,2,3, and 4 instead.

Good point -- will change.