Re: [PATCH v2] KVM: s390: fix LPSWEY handling

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

Am 01.07.24 um 08:08 schrieb Sven Schnelle:
> Christian Borntraeger <borntraeger@linux.ibm.com> writes:
> 
>> in rare cases, e.g. for injecting a machine check we do intercept all
>> load PSW instructions via ICTL_LPSW. With facility 193 a new variant
>> LPSWEY was added. KVM needs to handle that as well.
>>
>> Fixes: a3efa8429266 ("KVM: s390: gen_facilities: allow facilities 165, 193, 194 and 196")
>> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |  1 +
>>   arch/s390/kvm/kvm-s390.c         |  1 +
>>   arch/s390/kvm/kvm-s390.h         | 15 +++++++++++++++
>>   arch/s390/kvm/priv.c             | 32 ++++++++++++++++++++++++++++++++
>>   4 files changed, 49 insertions(+)
>>
>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>> index 1be19cc9d73c..1a49b89706f8 100644
>> --- a/arch/s390/kvm/priv.c
>> +++ b/arch/s390/kvm/priv.c
>> @@ -797,6 +797,36 @@ static int handle_lpswe(struct kvm_vcpu *vcpu)
>>   	return 0;
>>   }
>>   
>> +static int handle_lpswey(struct kvm_vcpu *vcpu)
>> +{
>> +	psw_t new_psw;
>> +	u64 addr;
>> +	int rc;
>> +	u8 ar;
>> +
>> +	vcpu->stat.instruction_lpswey++;
>> +
>> +	if (!test_kvm_facility(vcpu->kvm, 193))
>> +		return kvm_s390_inject_program_int(vcpu, PGM_OPERATION);
>> +
>> +	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>> +		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>> +
>> +	addr = kvm_s390_get_base_disp_siy(vcpu, &ar);
>> +	if (addr & 7)
>> +		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>> +
>> +	rc = read_guest(vcpu, addr, ar, &new_psw, sizeof(new_psw));
>> +	if (rc)
>> +		return kvm_s390_inject_prog_cond(vcpu, rc);
>> +
>> +	vcpu->arch.sie_block->gpsw = new_psw;
>> +	if (!is_valid_psw(&vcpu->arch.sie_block->gpsw))
>> +		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> 
> Shouldn't the gpsw get updated with new_psw after the check? POP says "The operation
> is suppressed on all addressing and protection exceptions."

Only for exception of the instruction but not for the target PSW.
POP says:

The other PSW fields which are to be loaded by the
instruction are not checked for validity before they are
loaded. However, immediately after loading, a speci-
fication exception is recognized, and a program inter-
ruption occurs, when any of the following is true for
the newly loaded PSW