Re: [PATCH v7 4/4] RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE

[Radim Krčmář]

2026-04-02T21:23:03+08:00, <fangyu.yu@xxxxxxxxxxxxxxxxx>:
> From: Fangyu Yu <fangyu.yu@xxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>
> Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>
> ---
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> @@ -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)
>  {
> +	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;

Since multiple VM ioctls can execute concurrently, I would protect
created_vcpus by kvm->lock and kvm_are_all_memslots_empty by
kvm->slots_lock.

Thanks.