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

[Anup Patel <anup@brainfault.org>]

On Fri, Dec 17, 2021 at 11:17 AM Atish Patra <atishp@atishpatra.org> wrote:
>
> On Mon, Nov 29, 2021 at 12:10 AM Anup Patel <anup.patel@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@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 ?

Okay, I will rename in the next revision.

Thanks,
Anup

>
> > 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@rivosinc.com>
>
>
> --
> Regards,
> Atish