Re: [PATCH v3 6/8] s390/sclp: add extended-length sccb support for kvm guest

[Thomas Huth <thuth@redhat.com>]

On 24/06/2020 16.57, Cornelia Huck wrote:
> On Wed, 24 Jun 2020 10:49:57 -0400
> Collin Walling <walling@linux.ibm.com> wrote:
> 
>> On 6/24/20 8:55 AM, Cornelia Huck wrote:
>>> On Wed, 24 Jun 2020 14:40:58 +0200
>>> Thomas Huth <thuth@redhat.com> wrote:
>>>    
>>>> On 24/06/2020 14.36, Cornelia Huck wrote:
>>>>> On Thu, 18 Jun 2020 18:22:56 -0400
>>>>> Collin Walling <walling@linux.ibm.com> wrote:
[...]
>>>>>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>>>>>> index 0dfbe6e5ec..f7c49e339e 100644
>>>>>> --- a/hw/s390x/sclp.c
>>>>>> +++ b/hw/s390x/sclp.c
>>>>>> @@ -56,6 +56,18 @@ static bool sccb_has_valid_boundary(uint64_t sccb_addr, uint32_t code,
>>>>>>        uint64_t sccb_boundary = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
>>>>>>    
>>>>>>        switch (code & SCLP_CMD_CODE_MASK) {
>>>>>> +    case SCLP_CMDW_READ_SCP_INFO:
>>>>>> +    case SCLP_CMDW_READ_SCP_INFO_FORCED:
>>>>>> +    case SCLP_CMDW_READ_CPU_INFO:
>>>>>> +        /*
>>>>>> +         * An extended-length SCCB is only allowed for Read SCP/CPU Info and
>>>>>> +         * is allowed to exceed the 4k boundary. The respective commands will
>>>>>> +         * set the length field to the required length if an insufficient
>>>>>> +         * SCCB length is provided.
>>>>>> +         */
>>>>>> +        if (s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB)) {
>>>>>> +            return true;
>>>>>> +        }
>>>>>
>>>>> Add a fallthrough annotation?
>>>>
>>>> ... otherwise Coverity and friends will complain later.
>>>
>>> Nod.
>>>    
>>
>> Something simple like...
>>
>> /* without this feature, these commands must respect the 4k boundary */
>>
>> ?
> 
> No, I meant something that is parsed by static checkers (/* fallthrough */
> seems to be the common marker for that in QEMU). I think what the
> fallthrough does is already clear enough to humans.

See also the "-Wimplicit-fallthrough" compiler option ... which we do 
not have enabled for QEMU yet, but maybe will be enabled one day. It can 
e.g. check for "/* fallthrough */" comments.

  Thomas