1. posterid:1775851
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Re: Hypervisor interrupt enables

Jonathan Behrens <behrensj@...>
 

Oh, good point. I'd forgotten about the hstatus.HU bit which gives U-mode the ability to do loads and stores in the VS-mode address space. U-mode still doesn't have access to the VS-mode CSRs (or virtual memory fence instructions AFAIK), but this does complicate the story.

On Mon, Mar 8, 2021 at 12:01 PM Scott Johnson via lists.riscv.org <scott.johnson=arilinc.com@...> wrote:
There is talk in the spec of running portions of the hypervisor code in U-mode.

On Mon, Mar 8, 2021 at 08:50 AM, Jonathan Behrens wrote:
I don't think calling U-mode more privileged than VS-mode is quite right either. U-mode software cannot access VS-mode CSRs for instance.
 
A different way of looking at it would be that VS-mode only exists when virtualization is enabled, so if you are running in U-mode (meaning virtualization is disabled) then VS-mode software cannot receive interrupts because there is no trap handler or other software configured for that mode.
 
Jonathan

On Mon, Mar 8, 2021 at 11:32 AM Scott Johnson via lists.riscv.org <scott.johnson=arilinc.com@...> wrote:
Ugh, correction: M > HS > U > VS > VU.

On Mon, Mar 8, 2021 at 08:27 AM, Scott Johnson wrote:

I would guess not...so the hierarchy is M > S > U > VS > VU.

 

 
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