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 15:39:14 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...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 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@...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?

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);
>>
>>
>