KVM: selftests: Create VM earlier for dirty log test

Since we've just removed the dependency of vm type in previous patch,
now we can create the vm much earlier.  Note that to move it earlier
we used an approximation of number of extra pages but it should be
fine.

This prepares for the follow up patches to finally remove the
duplication of guest mode parsings.
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/dirty_log_test.c

@@ -263,6 +263,9 @@ static struct kvm_vm *create_vm(enum vm_guest_mode mode, uint32_t vcpuid,
 	return vm;
 }
 
+#define DIRTY_MEM_BITS 30 /* 1G */
+#define PAGE_SHIFT_4K  12
+
 static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 		     unsigned long interval, uint64_t phys_offset)
 {
@@ -272,6 +275,18 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 	uint64_t max_gfn;
 	unsigned long *bmap;
 
+	/*
+	 * We reserve page table for 2 times of extra dirty mem which
+	 * will definitely cover the original (1G+) test range.  Here
+	 * we do the calculation with 4K page size which is the
+	 * smallest so the page number will be enough for all archs
+	 * (e.g., 64K page size guest will need even less memory for
+	 * page tables).
+	 */
+	vm = create_vm(mode, VCPU_ID,
+		       2ul << (DIRTY_MEM_BITS - PAGE_SHIFT_4K),
+		       guest_code);
+
 	switch (mode) {
 	case VM_MODE_P52V48_4K:
 		guest_pa_bits = 52;
@@ -318,7 +333,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 	 * A little more than 1G of guest page sized pages.  Cover the
 	 * case where the size is not aligned to 64 pages.
 	 */
-	guest_num_pages = (1ul << (30 - guest_page_shift)) + 16;
+	guest_num_pages = (1ul << (DIRTY_MEM_BITS - guest_page_shift)) + 16;
 #ifdef __s390x__
 	/* Round up to multiple of 1M (segment size) */
 	guest_num_pages = (guest_num_pages + 0xff) & ~0xffUL;
@@ -344,8 +359,6 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 	bmap = bitmap_alloc(host_num_pages);
 	host_bmap_track = bitmap_alloc(host_num_pages);
 
-	vm = create_vm(mode, VCPU_ID, guest_num_pages, guest_code);
-
 #ifdef USE_CLEAR_DIRTY_LOG
 	struct kvm_enable_cap cap = {};