Re: [PATCH v4 24/36] KVM: s390: protvirt: Do only reset registers that are accessible

Cornelia Huck
2020-02-25T13:16:42Z

On Tue, 25 Feb 2020 14:08:16 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 25.02.20 14:06, Cornelia Huck wrote:
> > On Tue, 25 Feb 2020 13:51:12 +0100
> > Janosch Frank <frankja@linux.ibm.com> wrote:
> >
> >> On 2/25/20 1:32 PM, Cornelia Huck wrote:
> >>> On Mon, 24 Feb 2020 06:40:55 -0500
> >>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >>>
> >>>> From: Janosch Frank <frankja@linux.ibm.com>
> >>>>
> >>>> For protected VMs the hypervisor can not access guest breaking event
> >>>> address, program parameter, bpbc and todpr. Do not reset those fields
> >>>> as the control block does not provide access to these fields.
> >>>>
> >>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> >>>> Reviewed-by: David Hildenbrand <david@redhat.com>
> >>>> [borntraeger@de.ibm.com: patch merging, splitting, fixing]
> >>>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >>>> ---
> >>>> arch/s390/kvm/kvm-s390.c | 10 ++++++----
> >>>> 1 file changed, 6 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> >>>> index 6ab4c88f2e1d..c734e89235f9 100644
> >>>> --- a/arch/s390/kvm/kvm-s390.c
> >>>> +++ b/arch/s390/kvm/kvm-s390.c
> >>>> @@ -3499,14 +3499,16 @@ static void kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
> >>>> kvm_s390_set_prefix(vcpu, 0);
> >>>> kvm_s390_set_cpu_timer(vcpu, 0);
> >>>> vcpu->arch.sie_block->ckc = 0;
> >>>> - vcpu->arch.sie_block->todpr = 0;
> >>>> memset(vcpu->arch.sie_block->gcr, 0, sizeof(vcpu->arch.sie_block->gcr));
> >>>> vcpu->arch.sie_block->gcr[0] = CR0_INITIAL_MASK;
> >>>> vcpu->arch.sie_block->gcr[14] = CR14_INITIAL_MASK;
> >>>> vcpu->run->s.regs.fpc = 0;
> >>>> - vcpu->arch.sie_block->gbea = 1;
> >>>> - vcpu->arch.sie_block->pp = 0;
> >>>> - vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
> >>>> + if (!kvm_s390_pv_cpu_is_protected(vcpu)) {
> >>>> + vcpu->arch.sie_block->gbea = 1;
> >>>> + vcpu->arch.sie_block->pp = 0;
> >>>> + vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
> >>>> + vcpu->arch.sie_block->todpr = 0;
> >>>
> >>> What happens if we do change those values? Is it just ignored or will
> >>> we get an exception on the next SIE entry?
> >>
> >> Well, changing gbea is a bad idea because of the sida overlay.
> >> I don't think that any other is checked, but I'd need to look up the
> >> todpr changes to be completely sure.
> >
> > Maybe add a comment
> >
> > /*
> > * Do not reset these registers in the protected case, as some of
> > * them are overlayed and they are not accessible in this case
> > * anyway.
> > */
>
> Makes sense, will add.
>

With that:

Reviewed-by: Cornelia Huck <cohuck@redhat.com>