How hvictl affect vstopi? Is every value legal?

[n1240549]

Hi @jhauser-us,
We have two question about HVICTL.

1. There is a candidate for vstopi, if bit 9 is not one in both vsip and vsie, hvictl.VTI=1, and hvictl.IID is not 9, the major interrupt is specified by hvictl field. Is it true that vstopi will reflect the value of hvictl no matter what value it contains? For example, what if the hvictl.iid is written with IID=MEI? (Machine External Interrupt should not be in VS-level).

if hvictl fields VTI = 1 and IID ̸= 9:
the major interrupt specified by hvictl fields IID, DPR, and IPRIO.

2. In spec, hvictl[27:16] is reserved for IID and the requirement is at least 6-bit. If the user choose to implement with 6-bit, could I say it's legal that hvictl[27:22] is always zero no matter what value is written to hvictl[27:22]?

IID is a WARL unsigned integer field with at least 6 implemented bits, while IPRIO is always the full 8 bits. If k bits are implemented for IID, then all values 0 through 2k − 1 are supported, and a write to hvictl sets IID equal to bits (15 + k):16 of the value written.

Thanks.

[jhauser-us]

1. ... Is it true that vstopi will reflect the value of hvictl no matter what value it contains?

Correct.

For example, what if the hvictl.iid is written with IID=MEI?

Then vstopi will indicate an MEI.

(Machine External Interrupt should not be in VS-level).

We leave it to hypervisor software to decide what interrupts a virtual machine may see. If a VM should not see an MEI, then the hypervisor should not inject an MEI into the VM. This is just one of many responsibilities that a hypervisor has in providing a valid RISC-V execution environment for a VM.

2. ... If the user choose to implement with 6-bit, could I say it's legal that hvictl[27:22] is always zero no matter what value is written to hvictl[27:22]?

Yes, definitely. Not only could you say it's legal; the part of the spec you quoted means to require exactly that.