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riscv / riscv-aia

https://jira.riscv.org/browse/RVG-59
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Is hstatus.VGEIN used to index guest interupt files when accessing iCSR via VSISELECT/VSIREG window? #99

Closed zengderui closed 1 week ago

zengderui commented 1 month ago

If I understand the spec correctly, each guest interrupt file has its own iCSR register file, and hstatus.VGEIN selects the iCSR file when VS-level iCSR files. E.g. when hstatus.VGEIN is 3 and VSISELECT is 0x70, accessing VSIREG ends up accessing eideilivery iCSR of guest interrupt file 3.

It seems the spec does not explicitly state how guest interrupt file is selected, I'd appreciate it if anyone clarifies it. Thanks in advance!

jhauser-us commented 1 week ago

In the IMSIC chapter, in the subsection titled "CSRs for external interrupts via an IMSIC", the AIA document says:

When an IMSIC has guest interrupt files, the VS CSRs interact with a single guest interrupt file, selected by the VGEIN field of CSR hstatus.

... when the hypervisor extension is implemented, there are three corresponding VS CSRs: vsiselect, vsireg, and vstopei.

... In each case, a value of the *iselect CSR (miselect, siselect, or vsiselect) in the range 0x70–0xFF selects a register of the corresponding IMSIC interrupt file, either the machine-level interrupt file (miselect), the supervisor-level interrupt file (siselect), or a guest interrupt file (vsiselect).

Maybe it's not easy to find, but I do think the AIA spec says hstatus.VGEIN selects the guest interrupt file that is accessed through registers vsiselect, vsireg, and vstopei.

zengderui commented 1 week ago

Thanks for clarifing!