Re: [Qemu-devel] [PATCH 1/4] s390: sclp base support

[Alexander Graf]

On 26.09.2012, at 18:06, Christian Borntraeger wrote:

> On 26/09/12 17:00, Alexander Graf wrote:
> 
>>> +/* Provide information about the configuration, CPUs and storage */
>>> +static void read_SCP_info(SCCB *sccb)
>>> +{
>>> +    ReadInfo *read_info = (ReadInfo *) sccb;
>>> +    int shift = 0;
>>> +
>>> +    while ((ram_size >> (20 + shift)) > 65535) {
>>> +        shift++;
>>> +    }
>>> +    read_info->rnmax = cpu_to_be16(ram_size >> (20 + shift));
>>> +    read_info->rnsize = 1 << shift;
>> 
>> Any reason we can't just always expose rnmax2 and rnsize2 instead? This way 
>> we're quite limited on the amount of RAM we can support, right?
> 
> Well, we have 65535 * 256 * 1MB == 16TB which is ok for the next 2 or 3 years 
> I guess.
> There are actually some rules that decide about rnmax vs rnmax2 etc, and here
> the non-2 are appropriate. This might change for systems > 16TB or systems 
> with memory hotplug,
> but I would prefer to use those for now. We will add the full logic in case 
> we add memory
> hotplug.

Fair enough :).

> 
> 
> [...]
> 
>>> +    if (be16_to_cpu(work_sccb.h.length) < 8 ||
>> 
>> sizeof(SCCBHeader)
> 
> ok
> 
> 
>> 
>>> +        be16_to_cpu(work_sccb.h.length) > 4096) {
>> 
>> SCCB_SIZE
> 
> ok
> 
> 
>>> */
>>> -int sclp_service_call(CPUS390XState *env, uint32_t sccb, uint64_t code)
>>> +int sclp_service_call(uint32_t sccb, uint64_t code)
>> 
>> Why not move the whole thing into sclp.c? The only thing remaining here are 
>> a few sanity checks that would just as well work in generic sclp handling 
>> code, right?
> 
> The idea was two-fold:
> - to have one single place were we cross between target-s390x and hw (review 
> feedback from the first series, originally we had all everything in sclp.c)
> - to have the checks that the CPU can do over there and the complex things 
> that look into the sccb in sclp.c
> 
> But we could certainly move that, your take

I would still see both fulfilled by having the 2 condition checks in sclp.c. 
Why don't we need them for kvm? Does kvm check them in the kernel?


Alex