Re: [RFC 26/37] KVM: s390: protvirt: Only sync fmt4 registers

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On 11/15/19 10:02 AM, Thomas Huth wrote:
> On 24/10/2019 13.40, Janosch Frank wrote:
>> A lot of the registers are controlled by the Ultravisor and never
>> visible to KVM. Also some registers are overlayed, like gbea is with
>> sidad, which might leak data to userspace.
>>
>> Hence we sync a minimal set of registers for both SIE formats and then
>> check and sync format 2 registers if necessary.
>>
>> Also we disable set/get one reg for the same reason. It's an old
>> interface anyway.
>>
>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>> ---
>>  arch/s390/kvm/kvm-s390.c | 138 +++++++++++++++++++++++----------------
>>  1 file changed, 82 insertions(+), 56 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 17a78774c617..f623c64aeade 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2997,7 +2997,8 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
>>  	/* make sure the new fpc will be lazily loaded */
>>  	save_fpu_regs();
>>  	current->thread.fpu.fpc = 0;
>> -	vcpu->arch.sie_block->gbea = 1;
>> +	if (!kvm_s390_pv_is_protected(vcpu->kvm))
>> +		vcpu->arch.sie_block->gbea = 1;
>>  	vcpu->arch.sie_block->pp = 0;
>>  	vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
>>  	vcpu->arch.pfault_token = KVM_S390_PFAULT_TOKEN_INVALID;
>> @@ -3367,6 +3368,10 @@ static int kvm_arch_vcpu_ioctl_get_one_reg(struct kvm_vcpu *vcpu,
>>  			     (u64 __user *)reg->addr);
>>  		break;
>>  	case KVM_REG_S390_GBEA:
>> +		if (kvm_s390_pv_is_protected(vcpu->kvm)) {
>> +			r = 0;
>> +			break;
>> +		}
>>  		r = put_user(vcpu->arch.sie_block->gbea,
>>  			     (u64 __user *)reg->addr);
>>  		break;
>> @@ -3420,6 +3425,10 @@ static int kvm_arch_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu,
>>  			     (u64 __user *)reg->addr);
>>  		break;
>>  	case KVM_REG_S390_GBEA:
>> +		if (kvm_s390_pv_is_protected(vcpu->kvm)) {
>> +			r = 0;
>> +			break;
>> +		}
> 
> Wouldn't it be better to return EINVAL in this case? ... the callers
> definitely do not get what they expected here...
> 
>  Thomas
> 

Hrm, new QEMUs will use cpu run anyway and hence I guess it would make
sense as old QEMUs hopefully won't have pv support.

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