KVM: selftests: arm64: Introduce a variable default IPA size

Contrary to popular belief, there is no such thing as a default
IPA size on arm64. Anything goes, and implementations are the
usual Wild West.

The selftest infrastructure default to 40bit IPA, which obviously
doesn't work for some systems out there.

Turn VM_MODE_DEFAULT from a constant into a variable, and let
guest_modes_append_default() populate it, depending on what
the HW can do. In order to preserve the current behaviour, we
still pick 40bits IPA as the default if it is available, and
the largest supported IPA space otherwise.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Link: https://lore.kernel.org/r/20211227124809.1335409-3-maz@kernel.org

tools/testing/selftests/kvm/include/kvm_util.h

@@ -53,7 +53,9 @@ enum vm_guest_mode {
 
 #if defined(__aarch64__)
 
-#define VM_MODE_DEFAULT			VM_MODE_P40V48_4K
+extern enum vm_guest_mode vm_mode_default;
+
+#define VM_MODE_DEFAULT			vm_mode_default
 #define MIN_PAGE_SHIFT			12U
 #define ptes_per_page(page_size)	((page_size) / 8)
 

tools/testing/selftests/kvm/lib/guest_modes.c

@@ -4,22 +4,46 @@
  */
 #include "guest_modes.h"
 
+#ifdef __aarch64__
+enum vm_guest_mode vm_mode_default;
+#endif
+
 struct guest_mode guest_modes[NUM_VM_MODES];
 
 void guest_modes_append_default(void)
 {
+#ifndef __aarch64__
 	guest_mode_append(VM_MODE_DEFAULT, true, true);
-
-#ifdef __aarch64__
-	guest_mode_append(VM_MODE_P40V48_64K, true, true);
+#else
 	{
 		unsigned int limit = kvm_check_cap(KVM_CAP_ARM_VM_IPA_SIZE);
+		int i;
+
+		vm_mode_default = NUM_VM_MODES;
+
 		if (limit >= 52)
 			guest_mode_append(VM_MODE_P52V48_64K, true, true);
 		if (limit >= 48) {
 			guest_mode_append(VM_MODE_P48V48_4K, true, true);
 			guest_mode_append(VM_MODE_P48V48_64K, true, true);
 		}
+		if (limit >= 40) {
+			guest_mode_append(VM_MODE_P40V48_4K, true, true);
+			guest_mode_append(VM_MODE_P40V48_64K, true, true);
+			vm_mode_default = VM_MODE_P40V48_4K;
+		}
+
+		/*
+		 * Pick the first supported IPA size if the default
+		 * isn't available.
+		 */
+		for (i = 0; vm_mode_default == NUM_VM_MODES && i < NUM_VM_MODES; i++) {
+			if (guest_modes[i].supported && guest_modes[i].enabled)
+				vm_mode_default = i;
+		}
+
+		TEST_ASSERT(vm_mode_default != NUM_VM_MODES,
+			    "No supported mode!");
 	}
 #endif
 #ifdef __s390x__