Re: [PATCH RFC 1/1] KVM: s390: Add MEMOP ioctl for reading/writing guest memory

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 04.02.2015 um 11:39 schrieb Paolo Bonzini:
>> Conny:
>> I am asking myself, if we should explicitly add a comment in the 
>> virtio-ccw spec, that all accesses are assumed to be with key 0 and 
>> thus never cause key protection. The change/reference bit is set
>> by the underlying I/O or memory copy anyway.
> 
> Can you explain the last sentence? :)

Whenever vhost or qemu or a finished aio request wrote content into a
virtio buffer, the HW has set the storage key for that physical page,
which  makes it automatically dirty/referenced in the guest visible
storage key. 


For completeness sake: 
Now, if the guest does not use the storage key, but instead the new fault
based software dirty tracking, it wont notice the change bit. The guest 
I/O itself when finished will mark the struct page as Dirty, just like on
x86.

Makes sense?

Christian