On Tue, Apr 29, 2025 at 3:55 PM Radim Krčmář <rkrcmar@xxxxxxxxxxxxxxxx> wrote: > > 2025-04-29T11:25:35+05:30, Anup Patel <apatel@xxxxxxxxxxxxxxxx>: > > 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. > > The initiating VCPU might not be the boot VCPU. > It would be safer to reset all of them. I meant initiating VCPU and not the boot VCPU. Currently, the non-initiating VCPUs are already resetted by VCPU requests so nothing special needs to be done. > > You also previously mentioned that we need to preserve the pre-reset > state for userspace, which I completely agree with and it is why the > reset happens later. Yes, that was only for debug purposes from user space. At the moment, there is no one using this for debug purposes so we can sacrifice that. > > > This way we also force KVM user-space to explicitly > > set the PC, A0, and A1 before running the VCPU again after > > system reset. > > We also want to consider reset from emulation outside of KVM. > > There is a "simple" solution that covers everything (except speed) -- > the userspace can tear down the whole VM and re-create it. > Do we want to do this instead and drop all resets from KVM? I think we should keep the VCPU resets in KVM so that handling of system reset handling in user space remains simple. The user space can also re-create the VM upon system reset but that is user space choice. Regards, Anup
