Re: [PATCH v2 1/2] KVM: s390: Don't indicate suppression on dirtying, failing memop

Janosch Frank
2022-04-26T13:39:26Z

On 4/26/22 15:25, Janis Schoetterl-Glausch wrote:
> On 4/26/22 09:18, Janosch Frank wrote:
>> On 4/25/22 12:01, Janis Schoetterl-Glausch wrote:
>>> If user space uses a memop to emulate an instruction and that
>>> memop fails, the execution of the instruction ends.
>>> Instruction execution can end in different ways, one of which is
>>> suppression, which requires that the instruction execute like a no-op.
>>
>>
>>
>>> A writing memop that spans multiple pages and fails due to key
>>> protection can modified guest memory, as a result, the likely
>>> correct ending is termination. Therefore do not indicate a
>>> suppressing instruction ending in this case.
>>
>> Check grammar.
>>
>>>
>>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>>> ---
>>>   arch/s390/kvm/gaccess.c | 47 ++++++++++++++++++++++++-----------------
>>>   1 file changed, 28 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
>>> index d53a183c2005..3b1fbef82288 100644
>>> --- a/arch/s390/kvm/gaccess.c
>>> +++ b/arch/s390/kvm/gaccess.c
>>> @@ -491,8 +491,8 @@ enum prot_type {
>>>       PROT_TYPE_IEP  = 4,
>>>   };
>>>   -static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>>> -             u8 ar, enum gacc_mode mode, enum prot_type prot)
>>> +static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva, u8 ar,
>>> +                enum gacc_mode mode, enum prot_type prot, bool suppress)
>>>   {
>>>       struct kvm_s390_pgm_info *pgm = &vcpu->arch.pgm;
>>>       struct trans_exc_code_bits *tec;
>>> @@ -503,22 +503,24 @@ static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>>>         switch (code) {
>>>       case PGM_PROTECTION:
>>> -        switch (prot) {
>>> -        case PROT_TYPE_IEP:
>>> -            tec->b61 = 1;
>>> -            fallthrough;
>>> -        case PROT_TYPE_LA:
>>> -            tec->b56 = 1;
>>> -            break;
>>> -        case PROT_TYPE_KEYC:
>>> -            tec->b60 = 1;
>>> -            break;
>>> -        case PROT_TYPE_ALC:
>>> -            tec->b60 = 1;
>>> -            fallthrough;
>>> -        case PROT_TYPE_DAT:
>>> -            tec->b61 = 1;
>>> -            break;
>>> +        if (suppress) {
>>> +            switch (prot) {
>>> +            case PROT_TYPE_IEP:
>>> +                tec->b61 = 1;
>>> +                fallthrough;
>>> +            case PROT_TYPE_LA:
>>> +                tec->b56 = 1;
>>> +                break;
>>> +            case PROT_TYPE_KEYC:
>>> +                tec->b60 = 1;
>>> +                break;
>>> +            case PROT_TYPE_ALC:
>>> +                tec->b60 = 1;
>>> +                fallthrough;
>>> +            case PROT_TYPE_DAT:
>>> +                tec->b61 = 1;
>>> +                break;
>>> +            }
>>>           }
>>
>> How about switching this around and masking those bits on termination.
>
> I did initially have if (!terminate) { ... }, but it seemed more straight forward
> to me without the negation. Or are you suggesting explicitly resetting the
> bits to zero when terminating?

Yes

>>
>>>           fallthrough;
>>>       case PGM_ASCE_TYPE:
>>> @@ -552,6 +554,12 @@ static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>>>       return code;
>>>   }
>>>   +static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva, u8 ar,
>>> +             enum gacc_mode mode, enum prot_type prot)
>>> +{
>>> +    return trans_exc_ending(vcpu, code, gva, ar, mode, prot, true);
>>> +}
>>> +
>>>   static int get_vcpu_asce(struct kvm_vcpu *vcpu, union asce *asce,
>>>                unsigned long ga, u8 ar, enum gacc_mode mode)
>>>   {
>>> @@ -1110,7 +1118,8 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>>>           ga = kvm_s390_logical_to_effective(vcpu, ga + fragment_len);
>>>       }
>>>       if (rc > 0)
>>> -        rc = trans_exc(vcpu, rc, ga, ar, mode, prot);
>>> +        rc = trans_exc_ending(vcpu, rc, ga, ar, mode, prot,
>>> +                      (mode != GACC_STORE) || (idx == 0));
>>
>> Add a boolean variable named terminating, calculate the value before passing the boolean on.
>
> Ok. I'll scope it to the body of the if.
>>
>>>   out_unlock:
>>>       if (need_ipte_lock)
>>>           ipte_unlock(vcpu);
>>
>>
>