The storage key is not part of the page table. However, when the OS pages something out, it has to record the key for the page frame so that it can restore the key when it reads the page back into a new page fram. How and where it records the key is up to the OS, not the architecture.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List [[email protected]] on behalf of Ian Worthington [[email protected]] Sent: Wednesday, November 23, 2022 5:12 AM To: [email protected] Subject: Re: Storage protection keys Many thanks for that Jay. This would certainly seem the logical place to store it. I'm still a bit confused though. The pop section on Page-Table Entries (page 3-51 in the 13th edition...) does not mention this (though it does have a unused byte at the end). If the intention is to make the storage key unaddressable (p 3-9) and alterable only via SSKE (which, given the need to propagate it to the caches of all processers would seem make sense) would it not be contraindicated to use this byte to keep it in? I'd love to see a paper or article which discusses how this is done, though, like cpu design, I appreciate it may well change from model to model. Best wishes Ian ... On Tuesday, November 22, 2022 at 05:28:37 PM GMT+1, Jay Maynard <[email protected]> wrote: They are held in the page tables and set in the hardware - in extra memory that is not software accessible except through a few supervisor-level instructions such as SSK (set storage key) - when the page is assigned to a real storage frame. On Tue, Nov 22, 2022 at 10:24 AM Ian Worthington < [email protected]> wrote: > I don't think the storage keys (and their friends) are held in the page > tables though. > > > Best wishes / Mejores deseos / Meilleurs vœux > > Ian ... > > On Tuesday, November 22, 2022 at 05:04:08 PM GMT+1, Jay Maynard < > [email protected]> wrote: > > Each page table entry has a byte associated with it that stores the key, > as > well as the referenced and changed bits. > > And yes, 4K page tables do soak up lots of memory, which is why later OSes > use 1M or 2M pages. > > On Tue, Nov 22, 2022 at 9:22 AM Ian Worthington < > [email protected]> wrote: > > > Does anyone know where the storage protection keys are kept? It seems > > that the processors maintain recent keys in the TLB to be accessed by the > > DAT, but where do they live when they're not in the TLB? Surely we need > > one byte per 4k page per address space, which could be quite a bit of > > storage, so I'm assuming this has to be above the bar now? I can't see > any > > information in the pop about this. > > > > > > Best wishes / Mejores deseos / Meilleurs vœux > > > > Ian ... > > > > ---------------------------------------------------------------------- > > For IBM-MAIN subscribe / signoff / archive access instructions, > > send email to [email protected] with the message: INFO IBM-MAIN > > > > > -- > Jay Maynard > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > -- Jay Maynard ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
