On Wednesday, 06/03/2015 at 02:08 EDT, Neale Ferguson <[email protected]> wrote: > Does zArchitecture still have semi-privileged instructions (I think > SSK/ISK were such beasts)? These were controlled via a control register > which made the instruction usable from userland. I thought this might be a > better option than another syscall as the last sentence means an app on > x86 will require more than just recompiling when porting to s390x. > However, given that z-MMIO uses special instructions that probably do not > have analogs in the non-z world the point is probably moot. Are these > instructions documented or are they less than open (like SIGA, SERVC, and > coupling instructions)?
I'm not aware of ever having semi-privileged instructions. An instruction is either available or not (availability may be under supervisor control). If available, it is either supervisor or problem state. (And I am admonished with sharp sticks wielded by the Defenders of the Architecture whenever I raise the idea of altering that model.) Maybe you are thinking of preferred guest I/O assists? If memory serves, CP had to identify a set of devices to which SIE could directly pass I/O requests with minimal checking, and without the help of CP. Devices not on that list would trigger a mandatory intercept. All of the instructions you mention are in the unpublished part of the architecture. But those instructions are really just frameworks that describe how to interact with the target device. The content of those interactions is, as with channel-attached devices, dependent on the target. And just as with modern FICON-attached devices, the device interface is not published. Since z I/O is offloaded to special-purpose I/O processors, there must then be a mechanism to engage them. Some signalling mechanism is needed. z's privileged I/O instructions are the things that do that. Alan Altmark Senior Managing z/VM and Linux Consultant Lab Services System z Delivery Practice IBM Systems & Technology Group ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 [email protected] IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
