On Mon, Apr 28, 2025 at 11:15 PM Radim Krčmář <rkrcmar@xxxxxxxxxxxxxxxx> wrote: > > 2025-04-28T17:52:25+05:30, Anup Patel <anup@xxxxxxxxxxxxxx>: > > On Thu, Apr 3, 2025 at 5:02 PM Radim Krčmář <rkrcmar@xxxxxxxxxxxxxxxx> 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? > Instead of creating a new interface, I would prefer that VCPU which initiates SBI System Reset should be resetted immediately in-kernel space before forwarding the system reset request to user space. This way we also force KVM user-space to explicitly set the PC, A0, and A1 before running the VCPU again after system reset. Regards, Anup
