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

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Date:   Tue, 26 Apr 2022 15:25:11 +0200
From:   Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
To:     Janosch Frank <frankja@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: s390: Don't indicate suppression on dirtying,
 failing memop

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@...ux.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?
> 
>>           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);
> 
>