Avi wrote:
There is an alternative, if you can recognize this condition exactly
from the hardware fault, you can fault the lowcore yourself and retry.
This eliminates a user interface. Is this workable?
I've read your comment again, and understood it this time. Trouble is
that the kernel cannot handle the situation either: userspace may need
to malloc some memory and call KVM_S390_UCAS_MAP prior to resolving it.
One could avoid the user interface by partially handling it in-kernel
and partially handling it in userspace without handshaking:
- user calls KVM_RUN
- SIE validity intercept
- kernel tries to gmap_fault and recognizes -EFAULT
- kernel returns validity intercept to user
- user does KVM_S390_UCAS_MAP
- user calls KVM_RUN
- SIE validity intercept
- kernel tries to gmap_fault and succeeds
- SIE runs ok

I guess I prefer to do processing of one operation in one place, and
thus I prefer the user interface over this. But yes, it'd be workable
without this interface. Is this what you want?

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