On Thursday, 03/17/2011 at 02:55 EDT, Shane G <[email protected]> wrote: > And which "real address 0" might that be ?. > Remembering that most people will be running as a guest under a hipervisor > (z/VM) running second level under another hipervisor (PR/SM).
That's a difference that makes no difference. For the purposes of booting, all "real" memory references are "absolute" since the prefix register of the IPL processor is zero. Once the kernel is loaded and starts running, it will eventually load each CPU's prefix register with a unique absolute address. At that point most memory references made by each CPU are done using "real" or "virtual" (collectively called "logical") addresses. Virtual addresses are converted to real addresses, and real addresses are converted to absolute addresses by application of the prefix register (for real addresses 0-8191). But these are just architectural concepts seen by the OS. As you note, when the camera pulls back, you discover that SIE was creating a useful lie, converting all those guest-absolute addresses to host-virtual, where the cycle begins again. Pull back again, and you find another instance of SIE with something called "zoning" and "address limiting". And you pull back once more only to find that the firmware maps absolute memory references made by "the machine" to physical memory modules located on the books, and that the mapping depends on the book configuration. The camera pulls back one last time and the cameraman falls off a cliff, interrupting the transmission. We don't know if the machine itself is virtual or not. We can't tell. (Though I did see a black cat walk by twice in a row....very suspicious....) Perspective is everything. Alan Altmark z/VM and Linux on System z Consultant IBM System Lab Services and Training 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/
