selftests: kvm: Add support for customized slot0 memory size

Until commit 39fe2fc96694 ("selftests: kvm: make allocation of extra
memory take effect", 2021-05-27), parameter extra_mem_pages was used
only to calculate the page table size for all the memory chunks,
because real memory allocation happened with calls of
vm_userspace_mem_region_add() after vm_create_default().

Commit 39fe2fc96694 however changed the meaning of extra_mem_pages to
the size of memory slot 0. This makes the memory allocation more
flexible, but makes it harder to account for the number of
pages needed for the page tables. For example, memslot_perf_test
has a small amount of memory in slot 0 but a lot in other slots,
and adding that memory twice (both in slot 0 and with later
calls to vm_userspace_mem_region_add()) causes an error that
was fixed in commit 000ac4295339 ("selftests: kvm: fix overlapping
addresses in memslot_perf_test", 2021-05-29)

Since both uses are sensible, add a new parameter slot0_mem_pages
to vm_create_with_vcpus() and some comments to clarify the meaning of
slot0_mem_pages and extra_mem_pages. With this change,
memslot_perf_test can go back to passing the number of memory
pages as extra_mem_pages.

Signed-off-by: Zhenzhong Duan <[e-mail]>
Message-Id: <[e-mail]>
[Squashed in a single patch and rewrote the commit message. - Paolo]
Signed-off-by: Paolo Bonzini <[e-mail]>

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

···
 					    uint32_t num_percpu_pages, void *guest_code,
 					    uint32_t vcpuids[]);
 
-/* Like vm_create_default_with_vcpus, but accepts mode as a parameter */
+/* Like vm_create_default_with_vcpus, but accepts mode and slot0 memory as a parameter */
 struct kvm_vm *vm_create_with_vcpus(enum vm_guest_mode mode, uint32_t nr_vcpus,
-				    uint64_t extra_mem_pages, uint32_t num_percpu_pages,
-				    void *guest_code, uint32_t vcpuids[]);
+				    uint64_t slot0_mem_pages, uint64_t extra_mem_pages,
+				    uint32_t num_percpu_pages, void *guest_code,
+				    uint32_t vcpuids[]);
 
 /*
  * Adds a vCPU with reasonable defaults (e.g. a stack)

tools/testing/selftests/kvm/kvm_page_table_test.c

···
 
 	/* Create a VM with enough guest pages */
 	guest_num_pages = test_mem_size / guest_page_size;
-	vm = vm_create_with_vcpus(mode, nr_vcpus,
+	vm = vm_create_with_vcpus(mode, nr_vcpus, DEFAULT_GUEST_PHY_PAGES,
 				  guest_num_pages, 0, guest_code, NULL);
 
 	/* Align down GPA of the testing memslot */

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

···
 	return vm;
 }
 
+/*
+ * VM Create with customized parameters
+ *
+ * Input Args:
+ *   mode - VM Mode (e.g. VM_MODE_P52V48_4K)
+ *   nr_vcpus - VCPU count
+ *   slot0_mem_pages - Slot0 physical memory size
+ *   extra_mem_pages - Non-slot0 physical memory total size
+ *   num_percpu_pages - Per-cpu physical memory pages
+ *   guest_code - Guest entry point
+ *   vcpuids - VCPU IDs
+ *
+ * Output Args: None
+ *
+ * Return:
+ *   Pointer to opaque structure that describes the created VM.
+ *
+ * Creates a VM with the mode specified by mode (e.g. VM_MODE_P52V48_4K),
+ * with customized slot0 memory size, at least 512 pages currently.
+ * extra_mem_pages is only used to calculate the maximum page table size,
+ * no real memory allocation for non-slot0 memory in this function.
+ */
 struct kvm_vm *vm_create_with_vcpus(enum vm_guest_mode mode, uint32_t nr_vcpus,
-				    uint64_t extra_mem_pages, uint32_t num_percpu_pages,
-				    void *guest_code, uint32_t vcpuids[])
+				    uint64_t slot0_mem_pages, uint64_t extra_mem_pages,
+				    uint32_t num_percpu_pages, void *guest_code,
+				    uint32_t vcpuids[])
 {
+	uint64_t vcpu_pages, extra_pg_pages, pages;
+	struct kvm_vm *vm;
+	int i;
+
+	/* Force slot0 memory size not small than DEFAULT_GUEST_PHY_PAGES */
+	if (slot0_mem_pages < DEFAULT_GUEST_PHY_PAGES)
+		slot0_mem_pages = DEFAULT_GUEST_PHY_PAGES;
+
 	/* The maximum page table size for a memory region will be when the
 	 * smallest pages are used. Considering each page contains x page
 	 * table descriptors, the total extra size for page tables (for extra
 	 * N pages) will be: N/x+N/x^2+N/x^3+... which is definitely smaller
 	 * than N/x*2.
 	 */
-	uint64_t vcpu_pages = (DEFAULT_STACK_PGS + num_percpu_pages) * nr_vcpus;
-	uint64_t extra_pg_pages = (extra_mem_pages + vcpu_pages) / PTES_PER_MIN_PAGE * 2;
-	uint64_t pages = DEFAULT_GUEST_PHY_PAGES + extra_mem_pages + vcpu_pages + extra_pg_pages;
-	struct kvm_vm *vm;
-	int i;
+	vcpu_pages = (DEFAULT_STACK_PGS + num_percpu_pages) * nr_vcpus;
+	extra_pg_pages = (slot0_mem_pages + extra_mem_pages + vcpu_pages) / PTES_PER_MIN_PAGE * 2;
+	pages = slot0_mem_pages + vcpu_pages + extra_pg_pages;
 
 	TEST_ASSERT(nr_vcpus <= kvm_check_cap(KVM_CAP_MAX_VCPUS),
 		    "nr_vcpus = %d too large for host, max-vcpus = %d",
···
 					    uint32_t num_percpu_pages, void *guest_code,
 					    uint32_t vcpuids[])
 {
-	return vm_create_with_vcpus(VM_MODE_DEFAULT, nr_vcpus, extra_mem_pages,
-				    num_percpu_pages, guest_code, vcpuids);
+	return vm_create_with_vcpus(VM_MODE_DEFAULT, nr_vcpus, DEFAULT_GUEST_PHY_PAGES,
+				    extra_mem_pages, num_percpu_pages, guest_code, vcpuids);
 }
 
 struct kvm_vm *vm_create_default(uint32_t vcpuid, uint64_t extra_mem_pages,

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

···
 	TEST_ASSERT(vcpu_memory_bytes % perf_test_args.guest_page_size == 0,
 		    "Guest memory size is not guest page size aligned.");
 
-	vm = vm_create_with_vcpus(mode, vcpus,
+	vm = vm_create_with_vcpus(mode, vcpus, DEFAULT_GUEST_PHY_PAGES,
 				  (vcpus * vcpu_memory_bytes) / perf_test_args.guest_page_size,
 				  0, guest_code, NULL);
 

tools/testing/selftests/kvm/memslot_perf_test.c

···
 	data->hva_slots = malloc(sizeof(*data->hva_slots) * data->nslots);
 	TEST_ASSERT(data->hva_slots, "malloc() fail");
 
-	data->vm = vm_create_default(VCPU_ID, 1024, guest_code);
+	data->vm = vm_create_default(VCPU_ID, mempages, guest_code);
 
 	pr_info_v("Adding slots 1..%i, each slot with %"PRIu64" pages + %"PRIu64" extra pages last\n",
 		max_mem_slots - 1, data->pages_per_slot, rempages);