Re: proposal to add "virtual instruction exception" to the hypervisor extension


Anup Patel
 

-----Original Message-----
From: tech-privileged@... <tech-privileged@...> On
Behalf Of Paolo Bonzini
Sent: 06 May 2020 14:34
To: John Hauser <jh.riscv@...>; tech-privileged@...
Subject: Re: [RISC-V] [tech-privileged] proposal to add "virtual instruction
exception" to the hypervisor extension

On 05/05/20 23:15, John Hauser wrote:
- attempts to execute WFI, unless the instruction completes within an
implementation-specific, bounded time;
It would be great to have this controlled by a bit in the hstatus CSR.
For example a hypervisor that does not overcommit CPUs will probably want
to delegate WFI to the guest. Guest-delegated interrupts then would not
incur the overhead of world switching, while host-handled interrupts would
exit to the hypervisor anyway.

(It may even make sense to add this to mstatus, but I wouldn't care much
about it right now except perhaps when choosing which bit to use in
hstatus).
Good suggestion.

A HSTATUS.VTW bit for trapping WFI when executed with V=1 would
be good (just like HSTATUS.VTSR and HSTATUS.VTVM bits) ?

Regards,
Anup

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