Re: [PATCH v4 09/10] RISC-V: KVM: Allow Smnpm and Ssnpm extensions for guests

[Anup Patel]

On Thu, Aug 29, 2024 at 6:32 AM Samuel Holland
<samuel.holland@xxxxxxxxxx> wrote:
>
> The interface for controlling pointer masking in VS-mode is henvcfg.PMM,
> which is part of the Ssnpm extension, even though pointer masking in
> HS-mode is provided by the Smnpm extension. As a result, emulating Smnpm
> in the guest requires (only) Ssnpm on the host.
>
> Since the guest configures Smnpm through the SBI Firmware Features
> interface, the extension can be disabled by failing the SBI call. Ssnpm
> cannot be disabled without intercepting writes to the senvcfg CSR.
>
> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
> ---
>
> (no changes since v2)
>
> Changes in v2:
>  - New patch for v2
>
>  arch/riscv/include/uapi/asm/kvm.h | 2 ++
>  arch/riscv/kvm/vcpu_onereg.c      | 3 +++
>  2 files changed, 5 insertions(+)
>
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index e97db3296456..4f24201376b1 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -175,6 +175,8 @@ enum KVM_RISCV_ISA_EXT_ID {
>         KVM_RISCV_ISA_EXT_ZCF,
>         KVM_RISCV_ISA_EXT_ZCMOP,
>         KVM_RISCV_ISA_EXT_ZAWRS,
> +       KVM_RISCV_ISA_EXT_SMNPM,
> +       KVM_RISCV_ISA_EXT_SSNPM,
>         KVM_RISCV_ISA_EXT_MAX,
>  };
>
> diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
> index b319c4c13c54..6f833ec2344a 100644
> --- a/arch/riscv/kvm/vcpu_onereg.c
> +++ b/arch/riscv/kvm/vcpu_onereg.c
> @@ -34,9 +34,11 @@ static const unsigned long kvm_isa_ext_arr[] = {
>         [KVM_RISCV_ISA_EXT_M] = RISCV_ISA_EXT_m,
>         [KVM_RISCV_ISA_EXT_V] = RISCV_ISA_EXT_v,
>         /* Multi letter extensions (alphabetically sorted) */
> +       [KVM_RISCV_ISA_EXT_SMNPM] = RISCV_ISA_EXT_SSNPM,

Why not use KVM_ISA_EXT_ARR() macro here ?

>         KVM_ISA_EXT_ARR(SMSTATEEN),
>         KVM_ISA_EXT_ARR(SSAIA),
>         KVM_ISA_EXT_ARR(SSCOFPMF),
> +       KVM_ISA_EXT_ARR(SSNPM),
>         KVM_ISA_EXT_ARR(SSTC),
>         KVM_ISA_EXT_ARR(SVINVAL),
>         KVM_ISA_EXT_ARR(SVNAPOT),
> @@ -129,6 +131,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
>         case KVM_RISCV_ISA_EXT_M:
>         /* There is not architectural config bit to disable sscofpmf completely */
>         case KVM_RISCV_ISA_EXT_SSCOFPMF:
> +       case KVM_RISCV_ISA_EXT_SSNPM:

Why not add KVM_RISCV_ISA_EXT_SMNPM here ?

Disabling Smnpm from KVM user space is very different from
disabling Smnpm from Guest using SBI FWFT extension.

The KVM user space should always add Smnpm in the
Guest ISA string whenever the Host ISA string has it.

The Guest must explicitly use SBI FWFT to enable
Smnpm only after it sees Smnpm in ISA string.

>         case KVM_RISCV_ISA_EXT_SSTC:
>         case KVM_RISCV_ISA_EXT_SVINVAL:
>         case KVM_RISCV_ISA_EXT_SVNAPOT:
> --
> 2.45.1
>
>
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Regards,
Anup