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

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Message-ID: <3c5472f4-44ce-9ba8-4dbc-967ea377ae10@redhat.com>
Date:   Fri, 17 Dec 2021 09:28:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Anup Patel <anup.patel@....com>, Shuah Khan <shuah@...nel.org>,
        Atish Patra <atishp@...shpatra.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/4] RISC-V: KVM: Add VM capability to allow userspace
 get GPA bits

On 11/29/21 08:54, Anup Patel 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@....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;
> +}
> 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
>   
> 

This is nice and other architectures could support it.

Paolo