KVM: selftests: Stop passing a memslot to nested_map_memslot()

On x86, KVM selftests use memslot 0 for all the default regions used by
the test infrastructure. This is an implementation detail.
nested_map_memslot() is currently used to map the default regions by
explicitly passing slot 0, which leaks the library implementation into
the caller.

Rename the function to a very verbose
nested_identity_map_default_memslots() to reflect what it actually does.
Add an assertion that only memslot 0 is being used so that the
implementation does not change from under us.

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251230230150.4150236-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: yosrym93

tools/testing/selftests/kvm/include/x86/vmx.h

@@ -563,8 +563,8 @@ void nested_pg_map(struct vmx_pages *vmx, struct kvm_vm *vm,
 		   uint64_t nested_paddr, uint64_t paddr);
 void nested_map(struct vmx_pages *vmx, struct kvm_vm *vm,
 		 uint64_t nested_paddr, uint64_t paddr, uint64_t size);
-void nested_map_memslot(struct vmx_pages *vmx, struct kvm_vm *vm,
-			uint32_t memslot);
+void nested_identity_map_default_memslots(struct vmx_pages *vmx,
+					  struct kvm_vm *vm);
 void nested_identity_map_1g(struct vmx_pages *vmx, struct kvm_vm *vm,
 			    uint64_t addr, uint64_t size);
 bool kvm_cpu_has_ept(void);

tools/testing/selftests/kvm/lib/x86/vmx.c

@@ -494,12 +494,16 @@ void nested_map(struct vmx_pages *vmx, struct kvm_vm *vm,
 /* Prepare an identity extended page table that maps all the
  * physical pages in VM.
  */
-void nested_map_memslot(struct vmx_pages *vmx, struct kvm_vm *vm,
-			uint32_t memslot)
+void nested_identity_map_default_memslots(struct vmx_pages *vmx,
+					  struct kvm_vm *vm)
 {
+	uint32_t s, memslot = 0;
 	sparsebit_idx_t i, last;
-	struct userspace_mem_region *region =
-		memslot2region(vm, memslot);
+	struct userspace_mem_region *region = memslot2region(vm, memslot);
+
+	/* Only memslot 0 is mapped here, ensure it's the only one being used */
+	for (s = 0; s < NR_MEM_REGIONS; s++)
+		TEST_ASSERT_EQ(vm->memslots[s], 0);
 
 	i = (region->region.guest_phys_addr >> vm->page_shift) - 1;
 	last = i + (region->region.memory_size >> vm->page_shift);

tools/testing/selftests/kvm/x86/vmx_dirty_log_test.c

@@ -121,7 +121,7 @@ static void test_vmx_dirty_log(bool enable_ept)
 	 */
 	if (enable_ept) {
 		prepare_eptp(vmx, vm);
-		nested_map_memslot(vmx, vm, 0);
+		nested_identity_map_default_memslots(vmx, vm);
 		nested_map(vmx, vm, NESTED_TEST_MEM1, GUEST_TEST_MEM, PAGE_SIZE);
 		nested_map(vmx, vm, NESTED_TEST_MEM2, GUEST_TEST_MEM, PAGE_SIZE);
 	}