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

Cornelia Huck
2020-02-25T12:33:05Z

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?

> + }
> }
>
> static void kvm_arch_vcpu_ioctl_clear_reset(struct kvm_vcpu *vcpu)