Re: [PATCH v2 26/42] KVM: s390: protvirt: Do only reset registers that are accessible

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 18.02.20 09:42, David Hildenbrand wrote:
> On 14.02.20 23:26, Christian Borntraeger 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>
>> [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 d20a7fa9d480..5b551cc73540 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -3442,14 +3442,16 @@ 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_handle_cpu(vcpu)) {
> 
> Shouldn't we instead check if the VM is in PV mode? (with changed
> lifecycle handling). Easier to understand.

No. these ioctls are under the vcpu->mutex, so I am going to compare
against the per cpu variant.

I will use kvm_s390_pv_cpu_is_protected instead to have the lockdep assertion.


> 
> (side not: the name kvm_s390_pv_handle_cpu() is very confusing. I'd
> suggest kvm_s390_pv_cpu_get_handle(). Will reply to the other patch)
> 
>> +		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;
>> +	}
>>  }
>>  
>>  static void kvm_arch_vcpu_ioctl_clear_reset(struct kvm_vcpu *vcpu)
>>
> 
>