Well, you have to store the key *somewhere* when the page is paged out. But you're right, the page table entry isn't it. I don't know what I was thinking.
I'm sure that VSM maintains its own table of correspondence between virtual storage addresses and storage key, so the key can be applied to the page upon page-in, but I don't know the details. On Wed, Nov 23, 2022 at 4:12 AM Ian Worthington < [email protected]> wrote: > 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 > -- Jay Maynard ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
