[PATCH v2 2/4] RISC-V: KVM: Add VM capability to allow userspace get GPA bits

[Atish Patra]

On Mon, Nov 29, 2021 at 12:10 AM Anup Patel <anup.patel at wdc.com> wrote:
>
> The number of GPA bits supported for a RISC-V Guest/VM is based on the
> MMU mode used by the G-stage translation. The KVM RISC-V will detect and
> use the best possible MMU mode for the G-stage in kvm_arch_init().
>
> We add a generic VM capability KVM_CAP_VM_GPA_BITS which can be used by
> the KVM userspace to get the number of GPA (guest physical address) bits
> supported for a Guest/VM.
>
> Signed-off-by: Anup Patel <anup.patel at wdc.com>
> ---
>  arch/riscv/include/asm/kvm_host.h | 1 +
>  arch/riscv/kvm/mmu.c              | 5 +++++
>  arch/riscv/kvm/vm.c               | 3 +++
>  include/uapi/linux/kvm.h          | 1 +
>  4 files changed, 10 insertions(+)
>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index 37589b953bcb..ae5d238607fe 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -221,6 +221,7 @@ void kvm_riscv_stage2_free_pgd(struct kvm *kvm);
>  void kvm_riscv_stage2_update_hgatp(struct kvm_vcpu *vcpu);
>  void kvm_riscv_stage2_mode_detect(void);
>  unsigned long kvm_riscv_stage2_mode(void);
> +int kvm_riscv_stage2_gpa_size(void);
>
>  void kvm_riscv_stage2_vmid_detect(void);
>  unsigned long kvm_riscv_stage2_vmid_bits(void);
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 9ffd0255af43..9b6d6465094f 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -760,3 +760,8 @@ unsigned long kvm_riscv_stage2_mode(void)
>  {
>         return stage2_mode >> HGATP_MODE_SHIFT;
>  }
> +
> +int kvm_riscv_stage2_gpa_size(void)
> +{
> +       return stage2_gpa_bits;
> +}

The ioctl & the underlying stage2_gpa_bits has bits.
Maybe rename the function to kvm_riscv_stage2_gpa_bits as well ?

> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> index fb18af34a4b5..6f959639ec45 100644
> --- a/arch/riscv/kvm/vm.c
> +++ b/arch/riscv/kvm/vm.c
> @@ -82,6 +82,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_NR_MEMSLOTS:
>                 r = KVM_USER_MEM_SLOTS;
>                 break;
> +       case KVM_CAP_VM_GPA_BITS:
> +               r = kvm_riscv_stage2_gpa_size();
> +               break;
>         default:
>                 r = 0;
>                 break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 1daa45268de2..469f05d69c8d 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>  #define KVM_CAP_ARM_MTE 205
>  #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
> +#define KVM_CAP_VM_GPA_BITS 207
>
>  #ifdef KVM_CAP_IRQ_ROUTING
>
> --
> 2.25.1
>

Other than that, it looks good to me.

Reviewed-by: Atish Patra <atishp at rivosinc.com>


-- 
Regards,
Atish