Re: [PATCH v2 4/7] KVM: selftests: Correctly initialize the VA space for TTBR0_EL1

[Paolo Bonzini]

On 12/9/22 02:53, Oliver Upton wrote:
> @@ -268,17 +305,17 @@ struct kvm_vm *____vm_create(enum vm_guest_mode mode)
>   #ifdef __aarch64__
>   	if (vm->pa_bits != 40)
>   		vm->type = KVM_VM_TYPE_ARM_IPA_SIZE(vm->pa_bits);
> +
> +	/* selftests use TTBR0 only, meaning there is a single VA region. */
> +	vm->has_split_va_space = false;
> +#else
> +	vm->has_split_va_space = true;
>   #endif
>   

Even though there happens to be already a suitable #ifdef, I don't
really like them and don't think there should be a new bool unless
something else uses it.

However, the new comment is very useful, so I added it to kvm_util.c as
follows:

/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 759a45540108..56d5ea949cbb 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -186,6 +186,15 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = {
 _Static_assert(sizeof(vm_guest_mode_params)/sizeof(struct vm_guest_mode_params) == NUM_VM_MODES,
 	       "Missing new mode params?");
 
+/*
+ * Initializes vm->vpages_valid to match the canonical VA space of the
+ * architecture.
+ *
+ * The default implementation is valid for architectures which split the
+ * range addressed by a single page table into a low and high region
+ * based on the MSB of the VA. On architectures with this behavior
+ * the VA region spans [0, 2^(va_bits - 1)), [-(2^(va_bits - 1), -1].
+ */
 __weak void vm_vaddr_populate_bitmap(struct kvm_vm *vm)
 {
 	sparsebit_set_num(vm->vpages_valid,