Re: [PATCH v7 10/45] arm64: kvm: Allow passing machine type in KVM creation

Gavin Shan
2025-03-03T04:54:06Z

On 2/14/25 2:13 AM, Steven Price wrote:
> Previously machine type was used purely for specifying the physical
> address size of the guest. Reserve the higher bits to specify an ARM
> specific machine type and declare a new type 'KVM_VM_TYPE_ARM_REALM'
> used to create a realm guest.
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v6:
> * Make the check for kvm_rme_is_available more visible and report an
> error code of -EPERM (instead of -EINVAL) to make it explicit that
> the kernel supports RME, but the platform doesn't.
> ---
> arch/arm64/kvm/arm.c | 15 +++++++++++++++
> arch/arm64/kvm/mmu.c | 3 ---
> include/uapi/linux/kvm.h | 19 +++++++++++++++----
> 3 files changed, 30 insertions(+), 7 deletions(-)
>

Section 4.2 of Documentation/virt/kvm/api.rst needs to be updated. Other
than that, it looks good to me:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index df6eb5e9ca96..917ee7c674f5 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -180,6 +180,21 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> mutex_unlock(&kvm->lock);
> #endif
>
> + if (type & ~(KVM_VM_TYPE_ARM_MASK | KVM_VM_TYPE_ARM_IPA_SIZE_MASK))
> + return -EINVAL;
> +
> + switch (type & KVM_VM_TYPE_ARM_MASK) {
> + case KVM_VM_TYPE_ARM_NORMAL:
> + break;
> + case KVM_VM_TYPE_ARM_REALM:
> + if (!static_branch_unlikely(&kvm_rme_is_available))
> + return -EPERM;
> + kvm->arch.is_realm = true;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> kvm_init_nested(kvm);
>
> ret = kvm_share_hyp(kvm, kvm + 1);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 8cda128aafef..f8ad8f88bbb8 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -886,9 +886,6 @@ static int kvm_init_ipa_range(struct kvm *kvm,
> if (kvm_is_realm(kvm))
> kvm_ipa_limit = kvm_realm_ipa_limit();
>
> - if (type & ~KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> - return -EINVAL;
> -
> phys_shift = KVM_VM_TYPE_ARM_IPA_SIZE(type);
> if (is_protected_kvm_enabled()) {
> phys_shift = kvm_ipa_limit;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index fa8f45029dff..9cabf9b6a9b4 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -644,14 +644,25 @@ struct kvm_enable_cap {
> #define KVM_S390_SIE_PAGE_OFFSET 1
>
> /*
> - * On arm64, machine type can be used to request the physical
> - * address size for the VM. Bits[7-0] are reserved for the guest
> - * PA size shift (i.e, log2(PA_Size)). For backward compatibility,
> - * value 0 implies the default IPA size, 40bits.
> + * On arm64, machine type can be used to request both the machine type and
> + * the physical address size for the VM.
> + *
> + * Bits[11-8] are reserved for the ARM specific machine type.
> + *
> + * Bits[7-0] are reserved for the guest PA size shift (i.e, log2(PA_Size)).
> + * For backward compatibility, value 0 implies the default IPA size, 40bits.
> */
> +#define KVM_VM_TYPE_ARM_SHIFT 8
> +#define KVM_VM_TYPE_ARM_MASK (0xfULL << KVM_VM_TYPE_ARM_SHIFT)
> +#define KVM_VM_TYPE_ARM(_type) \
> + (((_type) << KVM_VM_TYPE_ARM_SHIFT) & KVM_VM_TYPE_ARM_MASK)
> +#define KVM_VM_TYPE_ARM_NORMAL KVM_VM_TYPE_ARM(0)
> +#define KVM_VM_TYPE_ARM_REALM KVM_VM_TYPE_ARM(1)
> +
> #define KVM_VM_TYPE_ARM_IPA_SIZE_MASK 0xffULL
> #define KVM_VM_TYPE_ARM_IPA_SIZE(x) \
> ((x) & KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> +
> /*
> * ioctls for /dev/kvm fds:
> */

Thanks,
Gavin