Re: [PATCH v2 07/13] s390x: protvirt: SCLP interpretation

[David Hildenbrand <david@redhat.com>]

On 29.11.19 12:15, Janosch Frank wrote:
> On 11/29/19 11:43 AM, David Hildenbrand wrote:
>> On 29.11.19 10:48, Janosch Frank wrote:
>>> SCLP for a protected guest is done over the SIDAD, so we need to use
>>> the s390_cpu_virt_mem_* functions to access the SIDAD instead of guest
>>> memory when reading/writing SCBs.
>>
>> ... Can you elaborate a bit more how that is going to be used? Did you
>> hack in special memory access to something called "SIDAD" via
>> s390_cpu_virt_mem_*?
> 
> For secure guests we can't ever access virtual guest memory, since we
> have no access to the guest translation tables.
> 
> Hence we have the satellite block (SIDA) as a bounce buffer. SIE will
> bounce referenced blocks of data (like the SCCB) over the SIDA.
> 
> The virt_mem functions go through the KVM mem op API. A KVM patch
> reroutes mem op access to the SIDA. The alternative would be to map the
> SIDA into vcpu_run.
> 

I'd prefer *anything* over going via  s390_cpu_virt_mem_*, because as
you say "For secure guests we can't ever access virtual guest memory".
Introduce a new interface or go via vcpu_run. IMHO that's much cleaner.



-- 
Thanks,

David / dhildenb