IBM Mainframe Discussion List <[email protected]> wrote on 11/08/2007 07:20:09 PM:
> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Jim Mulder > Sent: Thursday, November 08, 2007 6:07 PM > To: [email protected] > Subject: Re: CSA 'above the bar' > > IBM Mainframe Discussion List <[email protected]> wrote on 11/08/2007 > 06:23:58 PM: > <SNIP> > Actually, no. We are talking about virtual addressability, and > x'000000' is certainly addressable as a 24-bit virtual address in every > address space, and addresses the PSA for the processor on which the code > is executing. > > Furthermore, absolute frame 0 is also addressable by using the SQA > virtual address of the PSA for the processor on which the code is > executing. This will reverse prefix to absolute 0. > As of z/OS 1.5, if there was more than one CPU available at IPL time, > the SQA virtual address of the a PSA will be a 31-bit ESQA address. > Otherwise, it will be a 24-bit SQA address. > > As of MVS/XA, we always use a non-zero prefix for each online CPU, so > practically speaking, MVS does not use frame absolute 0 for anything > other than IPL processing and SADMP processing (SADMP only uses one CPU > and uses a prefix of zero). > <SNIP> > > You did say dedicated. And it certainly appears to me to be both > dedicated and reserved (by architectural definition). > > In the MVS world, if a Problem State program attempts to modify 00000xxx > (where x is 0-512 decimal and regardless of the content of the current > base register) and LAP is on... So it is not truly available (except to > the SCP). Otherwise, as I recall [MVS environments], that page is Key0 > non-fetch protected. > > [The above is only for non-Z architected machines. I honestly haven't > read the requisite chapters in the new PoOP.] > 7FFFF000 is always not addressible in an MVS address space in 31-bit addressing mode because MVS chooses to never back that virtual page with a real page. The original poster asked if there is any address which has the same property in 24-bit addressing mode. The answer to that question is no. That is strictly an MVS implementation question. It is not a machine architecture question. I answered the original question from the point of view of what VSM does. However, I think a program can create an a page which is not addressable in 24-bit addressing mode by doing a GETMAIN or STORAGE OBTAIN with LOC=(24) to obtain a 24-bit virtual page address, and then using IARVSERV CHANGEACCESS,TARGET_VIEW=HIDDEN to make that page unaddressable. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
