Re: Fast-track extension proposal for "Hardware Performance Monitor count overflow and mode-based event filtering"

Greg Favor

On Mon, Feb 1, 2021 at 6:29 AM Phil McCoy <pnm@...> wrote:
Could you clarify how this extension interacts with mideleg?  I assume interrupt 13 would be taken in M-mode by default unless it is delegated to S-mode, but it would be nice to state this explicitly.

You're correct.  Standard mideleg functionality applies.  I'll incorporate a clarification note.
For implementations that support the Hypervisor extension, hideleg, hvip, hip, hie, vsip and vsie would also be of interest.

As you note, this starts getting into adding a number of bits and associated functionality.  The broader arch consistency question is whether this is the best path for the architecture going forward as other local interrupts come into being.

This has specifically been discussed with the lead Priv architects and the view is that there is a different and better way to support "delegation" of local interrupts into a VM.  (In particular, the new virtualization-aware next gen interrupt architecture will properly support this.  A working group on this will be starting shortly; I believe a public announcement is imminent.)


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