On Mon, May 26, 2025 at 2:52 PM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote: > > On Fri, May 23, 2025 at 01:33:49PM +0200, Radim Krčmář wrote: > > The new capability allows userspace to implement SBI extensions that KVM > > does not handle. This allows userspace to implement any SBI ecall as > > userspace already has the ability to disable acceleration of selected > > SBI extensions. > > The base extension is made controllable as well, but only with the new > > capability, because it was previously handled specially for some reason. > > *** The related compatibility TODO in the code needs addressing. *** > > > > This is a VM capability, because userspace will most likely want to have > > the same behavior for all VCPUs. We can easily make it both a VCPU and > > a VM capability if there is demand in the future. > > > > Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxxxxxxxx> > > --- > > v4: > > * forward base extension as well > > * change the id to 242, because 241 is already taken in linux-next > > * QEMU example: https://github.com/radimkrcmar/qemu/tree/mp_state_reset > > v3: new > > --- > > Documentation/virt/kvm/api.rst | 11 +++++++++++ > > arch/riscv/include/asm/kvm_host.h | 3 +++ > > arch/riscv/include/uapi/asm/kvm.h | 1 + > > arch/riscv/kvm/vcpu_sbi.c | 17 ++++++++++++++--- > > arch/riscv/kvm/vm.c | 5 +++++ > > include/uapi/linux/kvm.h | 1 + > > 6 files changed, 35 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > > index e107694fb41f..c9d627d13a5e 100644 > > --- a/Documentation/virt/kvm/api.rst > > +++ b/Documentation/virt/kvm/api.rst > > @@ -8507,6 +8507,17 @@ given VM. > > When this capability is enabled, KVM resets the VCPU when setting > > MP_STATE_INIT_RECEIVED through IOCTL. The original MP_STATE is preserved. > > > > +7.44 KVM_CAP_RISCV_USERSPACE_SBI > > +-------------------------------- > > + > > +:Architectures: riscv > > +:Type: VM > > +:Parameters: None > > +:Returns: 0 on success, -EINVAL if arg[0] is not zero > > + > > +When this capability is enabled, KVM forwards ecalls from disabled or unknown > > +SBI extensions to userspace. > > + > > 8. Other capabilities. > > ====================== > > > > diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h > > index 85cfebc32e4c..6f17cd923889 100644 > > --- a/arch/riscv/include/asm/kvm_host.h > > +++ b/arch/riscv/include/asm/kvm_host.h > > @@ -122,6 +122,9 @@ struct kvm_arch { > > > > /* KVM_CAP_RISCV_MP_STATE_RESET */ > > bool mp_state_reset; > > + > > + /* KVM_CAP_RISCV_USERSPACE_SBI */ > > + bool userspace_sbi; > > }; > > > > struct kvm_cpu_trap { > > diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h > > index 5f59fd226cc5..dd3a5dc53d34 100644 > > --- a/arch/riscv/include/uapi/asm/kvm.h > > +++ b/arch/riscv/include/uapi/asm/kvm.h > > @@ -204,6 +204,7 @@ enum KVM_RISCV_SBI_EXT_ID { > > KVM_RISCV_SBI_EXT_DBCN, > > KVM_RISCV_SBI_EXT_STA, > > KVM_RISCV_SBI_EXT_SUSP, > > + KVM_RISCV_SBI_EXT_BASE, > > KVM_RISCV_SBI_EXT_MAX, > > }; > > > > diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c > > index 31fd3cc98d66..497d5b023153 100644 > > --- a/arch/riscv/kvm/vcpu_sbi.c > > +++ b/arch/riscv/kvm/vcpu_sbi.c > > @@ -39,7 +39,7 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = { > > .ext_ptr = &vcpu_sbi_ext_v01, > > }, > > { > > - .ext_idx = KVM_RISCV_SBI_EXT_MAX, /* Can't be disabled */ > > + .ext_idx = KVM_RISCV_SBI_EXT_BASE, > > .ext_ptr = &vcpu_sbi_ext_base, > > }, > > { > > @@ -217,6 +217,11 @@ static int riscv_vcpu_set_sbi_ext_single(struct kvm_vcpu *vcpu, > > if (!sext || scontext->ext_status[sext->ext_idx] == KVM_RISCV_SBI_EXT_STATUS_UNAVAILABLE) > > return -ENOENT; > > > > + // TODO: probably remove, the extension originally couldn't be > > + // disabled, but it doesn't seem necessary > > + if (!vcpu->kvm->arch.userspace_sbi && sext->ext_id == KVM_RISCV_SBI_EXT_BASE) > > + return -ENOENT; > > + > > I agree that we don't need to babysit userspace and it's even conceivable > to have guests that don't need SBI. KVM should only need checks in its > UAPI to protect itself from userspace and to enforce proper use of the > API. It's not KVM's place to ensure userspace doesn't violate the SBI spec > or create broken guests (userspace is the boss, even if it's a boss that > doesn't make sense) > > So, I vote we drop the check. > > > scontext->ext_status[sext->ext_idx] = (reg_val) ? > > KVM_RISCV_SBI_EXT_STATUS_ENABLED : > > KVM_RISCV_SBI_EXT_STATUS_DISABLED; > > @@ -471,8 +476,14 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run) > > #endif > > ret = sbi_ext->handler(vcpu, run, &sbi_ret); > > } else { > > - /* Return error for unsupported SBI calls */ > > - cp->a0 = SBI_ERR_NOT_SUPPORTED; > > + if (vcpu->kvm->arch.userspace_sbi) { > > + next_sepc = false; > > + ret = 0; > > + kvm_riscv_vcpu_sbi_forward(vcpu, run); > > + } else { > > + /* Return error for unsupported SBI calls */ > > + cp->a0 = SBI_ERR_NOT_SUPPORTED; > > + } > > goto ecall_done; > > } > > > > diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c > > index b27ec8f96697..0b6378b83955 100644 > > --- a/arch/riscv/kvm/vm.c > > +++ b/arch/riscv/kvm/vm.c > > @@ -217,6 +217,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) > > return -EINVAL; > > kvm->arch.mp_state_reset = true; > > return 0; > > + case KVM_CAP_RISCV_USERSPACE_SBI: > > + if (cap->flags) > > + return -EINVAL; > > + kvm->arch.userspace_sbi = true; > > + return 0; > > default: > > return -EINVAL; > > } > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > > index 454b7d4a0448..bf23deb6679e 100644 > > --- a/include/uapi/linux/kvm.h > > +++ b/include/uapi/linux/kvm.h > > @@ -931,6 +931,7 @@ struct kvm_enable_cap { > > #define KVM_CAP_X86_GUEST_MODE 238 > > #define KVM_CAP_ARM_WRITABLE_IMP_ID_REGS 239 > > #define KVM_CAP_RISCV_MP_STATE_RESET 240 > > +#define KVM_CAP_RISCV_USERSPACE_SBI 242 > > > > struct kvm_irq_routing_irqchip { > > __u32 irqchip; > > -- > > 2.49.0 > > > > Otherwise, > > Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx> We are not going ahead with this approach for the reasons mentioned in v3 series [1]. Regards, Anup [1] https://patchwork.ozlabs.org/project/kvm-riscv/cover/20250515143723.2450630-4-rkrcmar@xxxxxxxxxxxxxxxx/
