Re: [RFC v1 07/25] target/arm/kvm: Create scratch Realm VM when requested

[Gavin Shan <gshan@redhat.com>]

On 7/8/26 8:42 AM, Mathieu Poirier wrote:
> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> When a Realm is requested, create a scratch Realm VM by setting bit 8
> of the argument given to the KVM_CREATE_VM ioctl().  Bit 7-0 are reserved
> for the guest PA size.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
>   target/arm/kvm-rme.c  | 8 ++++++++
>   target/arm/kvm-stub.c | 5 +++++
>   target/arm/kvm.c      | 4 +++-
>   target/arm/kvm_arm.h  | 8 ++++++++
>   4 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/target/arm/kvm-rme.c b/target/arm/kvm-rme.c
> index 90c1d30ba24c..f763d5ed6199 100644
> --- a/target/arm/kvm-rme.c
> +++ b/target/arm/kvm-rme.c
> @@ -99,3 +99,11 @@ void kvm_arm_rme_vcpu_init(ARMCPU *cpu)
>   
>       cpu->kvm_rme = true;
>   }
> +
> +int kvm_arm_rme_vm_type(void)
> +{
> +    if (rme_guest) {
> +        return KVM_VM_TYPE_ARM_REALM;
> +    }
> +    return 0;
> +}

We had official name for 0, which is KVM_VM_TYPE_ARM_NORMAL. Another question if
it's worthwhile to have this helper since it's equivalent to something as below,
which can be directly applied to the caller.


     int vm_type = (current_machine && current_machine->cgs) ? KVM_VM_TYPE_ARM_REALM :
                                                               KVM_VM_TYPE_ARM_NORMAL;


> diff --git a/target/arm/kvm-stub.c b/target/arm/kvm-stub.c
> index 4ab6f08637d1..6d52f172c5df 100644
> --- a/target/arm/kvm-stub.c
> +++ b/target/arm/kvm-stub.c
> @@ -129,3 +129,8 @@ void kvm_arm_rme_vcpu_init(ARMCPU *cpu)
>   {
>       g_assert_not_reached();
>   }
> +
> +int kvm_arm_rme_vm_type(void)
> +{
> +    g_assert_not_reached();
> +}
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 4c212ed0c337..6aa1cd04e484 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -108,6 +108,7 @@ bool kvm_arm_create_scratch_host_vcpu(int *fdarray,
>   {
>       int ret = 0, kvmfd = -1, vmfd = -1, cpufd = -1;
>       int max_vm_pa_size;
> +    int vm_type;
>   
>       kvmfd = qemu_open_old("/dev/kvm", O_RDWR);
>       if (kvmfd < 0) {
> @@ -117,8 +118,9 @@ bool kvm_arm_create_scratch_host_vcpu(int *fdarray,
>       if (max_vm_pa_size < 0) {
>           max_vm_pa_size = 0;
>       }
> +    vm_type = kvm_arm_rme_vm_type();
>       do {
> -        vmfd = ioctl(kvmfd, KVM_CREATE_VM, max_vm_pa_size);
> +        vmfd = ioctl(kvmfd, KVM_CREATE_VM, max_vm_pa_size | vm_type);
>       } while (vmfd == -1 && errno == EINTR);
>       if (vmfd < 0) {
>           goto err;
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index 12ed1eee18b4..65ec1b970606 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -259,4 +259,12 @@ int kvm_arm_rme_init(MachineState *ms, KVMState *s);
>    */
>   void kvm_arm_rme_vcpu_init(ARMCPU *cpu);
>   
> +/**
> + * kvm_arm_rme_vm_type
> + * @ms: the machine state
> + *
> + * Returns the Realm KVM VM type if the user requested a Realm, 0 otherwise.
> + */
> +int kvm_arm_rme_vm_type(void);
> +
>   #endif

Thanks,
Gavin