[PATCH v6 4/4] RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE

[Guo Ren]

On Mon, Mar 30, 2026 at 8:26 PM <fangyu.yu at linux.alibaba.com> wrote:
>
> From: Fangyu Yu <fangyu.yu at linux.alibaba.com>
>
> Add a VM capability that allows userspace to select the G-stage page table
> format by setting HGATP.MODE on a per-VM basis.
>
> Userspace enables the capability via KVM_ENABLE_CAP, passing the requested
> HGATP.MODE in args[0]. The request is rejected with -EINVAL if the mode is
> not supported by the host, and with -EBUSY if the VM has already been
> committed (e.g. vCPUs have been created or any memslot is populated).
>
> KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE) returns a bitmask of the
> HGATP.MODE formats supported by the host.
>
> Signed-off-by: Fangyu Yu <fangyu.yu at linux.alibaba.com>
> Reviewed-by: Andrew Jones <andrew.jones at oss.qualcomm.com>
> ---
>  Documentation/virt/kvm/api.rst | 27 +++++++++++++++++++++++++++
>  arch/riscv/kvm/vm.c            | 18 ++++++++++++++++--
>  include/uapi/linux/kvm.h       |  1 +
>  3 files changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 032516783e96..9d7f6958fa81 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -8902,6 +8902,33 @@ helpful if user space wants to emulate instructions which are not
>  This capability can be enabled dynamically even if VCPUs were already
>  created and are running.
>
> +7.47 KVM_CAP_RISCV_SET_HGATP_MODE
> +---------------------------------
> +
> +:Architectures: riscv
> +:Type: VM
> +:Parameters: args[0] contains the requested HGATP mode
> +:Returns:
> +  - 0 on success.
> +  - -EINVAL if args[0] is outside the range of HGATP modes supported by the
> +    hardware.
> +  - -EBUSY if vCPUs have already been created for the VM, if the VM has any
> +    non-empty memslots.
> +
> +This capability allows userspace to explicitly select the HGATP mode for
> +the VM. The selected mode must be supported by both KVM and hardware. This
> +capability must be enabled before creating any vCPUs or memslots.
> +
> +If this capability is not enabled, KVM will select the default HGATP mode
> +automatically. The default is the highest HGATP.MODE value supported by
> +hardware.
> +
> +``KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE)`` returns a bitmask of
> +HGATP.MODE values supported by the host. A return value of 0 indicates that
> +the capability is not supported. Supported-mode bitmask use HGATP.MODE
> +encodings as defined by the RISC-V privileged specification, such as Sv39x4
> +corresponds to HGATP.MODE=8, so userspace should test bitmask & BIT(8).
> +
>  8. Other capabilities.
>  ======================
>
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> index 4d82a886102c..5e82a3ad3ad0 100644
> --- a/arch/riscv/kvm/vm.c
> +++ b/arch/riscv/kvm/vm.c
> @@ -201,6 +201,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_VM_GPA_BITS:
>                 r = kvm_riscv_gstage_gpa_bits(kvm->arch.pgd_levels);
>                 break;
> +       case KVM_CAP_RISCV_SET_HGATP_MODE:
> +               r = kvm_riscv_get_hgatp_mode_mask();
> +               break;
>         default:
>                 r = 0;
>                 break;
> @@ -211,12 +214,23 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>
>  int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>  {
> +       if (cap->flags)
> +               return -EINVAL;
> +
>         switch (cap->cap) {
>         case KVM_CAP_RISCV_MP_STATE_RESET:
> -               if (cap->flags)
> -                       return -EINVAL;
>                 kvm->arch.mp_state_reset = true;
>                 return 0;
> +       case KVM_CAP_RISCV_SET_HGATP_MODE:
> +               if (!kvm_riscv_hgatp_mode_is_valid(cap->args[0]))
> +                       return -EINVAL;
> +
> +               if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm))
> +                       return -EBUSY;
> +#ifdef CONFIG_64BIT
> +               kvm->arch.pgd_levels = 3 + cap->args[0] - HGATP_MODE_SV39X4;
> +#endif
> +               return 0;
>         default:
>                 return -EINVAL;
>         }
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 80364d4dbebb..a74a80fd4046 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -989,6 +989,7 @@ struct kvm_enable_cap {
>  #define KVM_CAP_ARM_SEA_TO_USER 245
>  #define KVM_CAP_S390_USER_OPEREXEC 246
>  #define KVM_CAP_S390_KEYOP 247
> +#define KVM_CAP_RISCV_SET_HGATP_MODE 248
>
>  struct kvm_irq_routing_irqchip {
>         __u32 irqchip;
> --
> 2.50.1
>
Reviewed-by: Guo Ren <guoren at kernel.org>

-- 
Best Regards
 Guo Ren