On 16 February 2016 at 11:31, Joel C. Ewing <[email protected]> wrote: > That seems pretty explicit to me that the plan is that on z14 and beyond > an operating system will be required to start and run exclusively in > z/Architecture mode and that there will simply be no hardware capability > to run in ESA/390 mode, period.
Yup - I'm now convinced. Jim Mulder said "Well, for one thing, there won't be any ESA/390 mode Dynamic Address Translation, either at SIE Guest 1 (in an LPAR) or at Guest 2 (under VM). So you certainly will not be able to run any operating system that uses ESA/390 virtual addressing, even under VM." That's quite definitive enough for me. I do think IBM could've been somewhat clearer with their announcements. On a z13 or earlier it's certainly possible to run z/VM entirely in zArch mode (after the initial and brief IPL sequence) without ever switching the archmode back to ESA/390, and yet run ESA/390 guests using SIE. For performance reasons alone, it is implausible that zSIE would internally issue SIGP to set the archmode to ESA/390 every time it dispatches an ESA/390 guest, so presumably there is code in SIE that either exploits an underlying ESA/390 DAT facility, and probably other ESA/390 things I haven't thought about, all while remaining in zArch mode, or maintains shadow DAT tables to map between guest ESA/390 and host zArch DAT. I don't know if the latter is architecturally possible with the current definitions, but it's not immediately out of the question. What Jim has now said clearly is that IBM will remove the ability to perform ESA/390 DAT entirely at any SIE level in z14+. Presumably issuing SIE with a SIE block indicating ESA/390 archmode will simply fail, and it's game over. The remaining question of interest is the fate of XC mode and a putative zXC mode on these new machines. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
