tech-privileged@lists.riscv.org

Home Messages Hashtags Subgroups

Messages

Topics Expanded Polls

Export Group Data

Between

and

Re: proposal for stateen CSRs

Oooh. I think I got you now. How would the S-mode software enable all the custom enable bits in those custom CSRs?

By Scott Johnson · #593 ·

Re: proposal for stateen CSRs

The M-mode software would write a 1 to that bit?

By Scott Johnson · #592 ·

Re: proposal for stateen CSRs

Scott Johnson wrote: How would that allow one to enable lower-privilege access to all unknown custom state? You said yourself earlier: - John Hauser

By John Hauser · #591 ·

Re: proposal for stateen CSRs

The more bits we dedicate to custom use to ensure that we've got enough for everyone, the quicker we use up each *stateen CSR, when we can be pretty sure most of those custom bits will be unused in

By John Hauser · #590 ·

Re: proposal for stateen CSRs

Code that does environment swapping will need to use custom instructions to save custom state, so might as well use custom CSRs for the individual enable bits instead of taking up space in the

By Scott Johnson · #589 ·

Re: proposal for stateen CSRs

Why does all custom state need to be controlled with a single bit? Couldn't we just designate the upper 8 or 16 bits of each xstateenY register to be custom? Any software that wanted to disable all

By Jonathan Behrens <behrensj@...> · #588 ·

Re: proposal for stateen CSRs

Allen Baum wrote: It provides a convenient means for software to enable lower-privilege access to all custom state, requiring only the minimal amount of hardware for the task. - John Hauser

By John Hauser · #587 ·

Re: proposal for stateen CSRs

Like Allen, I'm not following the need for this complexity. Why not one simple read/write bit that disables all custom state when 0? It would be ANDed with any custom state enable CSR bits, much like

By Scott Johnson · #586 ·

Re: proposal for stateen CSRs

If I understand the above: you can write a 1 to the first bit, but you'll always read back zero? What does that accomplish? I think you need to establish what the (legal) reset state(s) is/are

By Allen Baum · #585 ·

Re: proposal for stateen CSRs

Having a more misa-like implementation would also allow virtualization of an implementation without support for a particular stateless extension such as A or B, though it would take more bits. Via

By Paul Donahue · #584 ·

Re: proposal for stateen CSRs

I wrote: Scott Johnson: After I wrote my earlier message, I realized we need to be able to revoke permissions, and this is best supported with a second bit alongside the first one. The second bit

By John Hauser · #583 ·

Re: proposal for stateen CSRs

Jonathan Behrens wrote: That would be true, except we already have the "H" bit in misa which is expected to be writable. Also, to ease future hardware support for nested hypervisors, it turns out the

By John Hauser · #582 ·

Re: proposal for stateen CSRs

I agree one bit is sufficient, but I don’t understand the write-only, read-zero behavior? Would M-mode never be able to revoke permissions?

By Scott Johnson · #581 ·

Re: proposal for stateen CSRs

By Bill Huffman · #580 ·

Re: proposal for stateen CSRs

The proposed mstateenX CSRs feels very similar to misa. It almost seems like you could achieve the same thing as this proposal just by adding sisa and hisa (plus misa2, misa3, ...), but I think I've

By Jonathan Behrens <behrensj@...> · #579 ·

Re: proposal for stateen CSRs

Allen Baum wrote: I forgot to say what that means, didn't I? Good point! To quote Admiral Ackbar: "It's a trap!" You get an illegal instruction trap, unless you're executing in a virtual machine

By John Hauser · #578 ·

Re: proposal for stateen CSRs

Scott Johnson wrote: Yes, that's exactly what we were thinking. This seems like a sensible request to me, except I would accomplish the same effect by adding a single "write-only" bit to mstateen0.

By John Hauser · #577 ·

Re: proposal for stateen CSRs

Questions: (I suspect I know the answers, but want to be clear): -if mstateenY[n] is cleared, and s-mode code tries to read/write a CSR that is controlled by that bit -- does the access trap?

By Allen Baum · #576 ·

Re: proposal for stateen CSRs

It seems the use model is to enable older environment-swapping software to run on newer hardware without opening a security hole via new state. Only if the software is aware of the state will it

By Scott Johnson · #575 ·

Re: proposal for stateen CSRs

Hello John, Are some of the bits in xstateen allocated for custom use? Bill

By Bill Huffman · #574 ·

741 - 760 of 1333

Home Hashtags Subgroups Terms