[PATCH 3/3] RISC-V: KVM: Introduce extension_enabled

[Anup Patel]

On Wed, Apr 26, 2023 at 10:43 PM Andrew Jones <ajones at ventanamicro.com> wrote:
>
> We need three SBI extension status values (uninitialized, enabled,
> and disabled). Pairing another boolean array, extension_enabled[],
> with the boolean array extension_disabled[] provides four states.
> Using a pair of boolean arrays, which may eventually be changed to
> a pair of bitmaps, is more space efficient than using one enum
> status field. Apply the new (enabled=1,disabled=0) state, which
> means either the extension doesn't have a probe function or that
> its probe was successful, to avoid more than one probe of the
> extension.
>
> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_sbi.h |  9 +++++++++
>  arch/riscv/kvm/vcpu_sbi.c             | 11 ++++++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index 4278125a38a5..e3c5e1d15e93 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -16,6 +16,15 @@
>
>  struct kvm_vcpu_sbi_context {
>         int return_handled;
> +       /*
> +        * extension_enabled[] and extension_disabled[] provide SBI
> +        * extensions four status values, of which we need three:
> +        * (0,0) uninitialized, (1,0) enabled, (0,1) disabled. Using
> +        * a pair of boolean arrays, which may eventually be changed
> +        * to a pair of bitmaps, is more space efficient than using
> +        * one enum status field.
> +        */
> +       bool extension_enabled[KVM_RISCV_SBI_EXT_MAX];

The extension_enabled[] is not an appropriate name.

How about extension_probe_allowed[] ?

Any better name ?

Regards,
Anup

>         bool extension_disabled[KVM_RISCV_SBI_EXT_MAX];
>  };
>
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index a1a82f0fbad2..344d38bbe06a 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -155,6 +155,12 @@ static int riscv_vcpu_set_sbi_ext_single(struct kvm_vcpu *vcpu,
>         if (!sext)
>                 return -ENOENT;
>
> +       /*
> +        * We can't set scontext->extension_enabled[] to reg_val since the
> +        * extension may have a probe() function which needs to confirm
> +        * enablement first. Only set extension_disabled[] here and leave
> +        * the extension_enabled[] setting to kvm_vcpu_sbi_find_ext().
> +        */
>         scontext->extension_disabled[sext->ext_idx] = !reg_val;
>
>         return 0;
> @@ -317,7 +323,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
>                 ext = entry->ext_ptr;
>
>                 if (ext->extid_start <= extid && ext->extid_end >= extid) {
> -                       if (entry->ext_idx >= KVM_RISCV_SBI_EXT_MAX)
> +                       if (entry->ext_idx >= KVM_RISCV_SBI_EXT_MAX ||
> +                           scontext->extension_enabled[entry->ext_idx])
>                                 return ext;
>                         if (scontext->extension_disabled[entry->ext_idx])
>                                 return NULL;
> @@ -325,6 +332,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
>                                 scontext->extension_disabled[entry->ext_idx] = true;
>                                 return NULL;
>                         }
> +
> +                       scontext->extension_enabled[entry->ext_idx] = true;
>                         return ext;
>                 }
>         }
> --
> 2.39.2
>