Subject: Re: [PATCH v17 23/24] KVM: selftests: guest_memfd mmap() test when mmap is supported

From: Xiaoyao Li <[email-masked]>
Date: Wed, 30 Jul 2025 19:39:41 +0800

On 7/30/2025 6:54 AM, Sean Christopherson wrote:

...

> +int main(int argc, char *argv[])
> +{
> +	unsigned long vm_types, vm_type;
> +
> +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
> +
> +	/*
> +	 * Not all architectures support KVM_CAP_VM_TYPES. However, those that
> +	 * support guest_memfd have that support for the default VM type.
> +	 */
> +	vm_types = kvm_check_cap(KVM_CAP_VM_TYPES);
> +	if (!vm_types)
> +		vm_types = VM_TYPE_DEFAULT;
> +
> +	for_each_set_bit(vm_type, &vm_types, BITS_PER_TYPE(vm_types))
> +		test_guest_memfd(vm_type);

For ARCHes that don't support KVM_CAP_VM_TYPES, e.g., ARM, vm_types is 0 
(VM_TYPE_DEFAULT). the for_each_set_bit() loop will not execute any 
iteration at all.