[PATCH 4/5] KVM: RISC-V: reset VCPU state when becoming runnable

[Radim Krčmář]

2025-04-28T17:52:25+05:30, Anup Patel <anup at brainfault.org>:
> On Thu, Apr 3, 2025 at 5:02 PM Radim Krčmář <rkrcmar at ventanamicro.com> wrote:
>> For a cleaner solution, we should add interfaces to perform the KVM-SBI
>> reset request on userspace demand.  I think it would also be much better
>> if userspace was in control of the post-reset state.
>
> Apart from breaking KVM user-space, this patch is incorrect and
> does not align with the:
> 1) SBI spec
> 2) OS boot protocol.
>
> The SBI spec only defines the entry state of certain CPU registers
> (namely, PC, A0, and A1) when CPU enters S-mode:
> 1) Upon SBI HSM start call from some other CPU
> 2) Upon resuming from non-retentive SBI HSM suspend or
>     SBI system suspend
>
> The S-mode entry state of the boot CPU is defined by the
> OS boot protocol and not by the SBI spec. Due to this, reason
> KVM RISC-V expects user-space to set up the S-mode entry
> state of the boot CPU upon system reset.

We can handle the initial state consistency in other patches.
What needs addressing is a way to trigger the KVM reset from userspace,
even if only to clear the internal KVM state.

I think mp_state is currently the best signalization that KVM should
reset, so I added it there.

What would be your preferred interface for that?

Thanks.