KVM: selftests: Drop DEFAULT_GUEST_PHY_PAGES, open code the magic number

Remove DEFAULT_GUEST_PHY_PAGES and open code the magic number (with a
comment) in vm_nr_pages_required(). Exposing DEFAULT_GUEST_PHY_PAGES to
tests was a symptom of the VM creation APIs not cleanly supporting tests
that create runnable vCPUs, but can't do so immediately. Now that tests
don't have to manually compute the amount of memory needed for basic
operation, make it harder for tests to do things that should be handled
by the framework, i.e. force developers to improve the framework instead
of hacking around flaws in individual tests.

Signed-off-by: Sean Christopherson <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

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

···
 #define KVM_UTIL_MIN_VADDR		0x2000
 #define KVM_GUEST_PAGE_TABLE_MIN_PADDR	0x180000
 
-#define DEFAULT_GUEST_PHY_PAGES		512
 #define DEFAULT_GUEST_STACK_VADDR_MIN	0xab6000
 #define DEFAULT_STACK_PGS		5
 

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

···
 		    "nr_vcpus = %d too large for host, max-vcpus = %d",
 		    nr_runnable_vcpus, kvm_check_cap(KVM_CAP_MAX_VCPUS));
 
-	nr_pages = DEFAULT_GUEST_PHY_PAGES;
+	/*
+	 * Arbitrarily allocate 512 pages (2mb when page size is 4kb) for the
+	 * test code and other per-VM assets that will be loaded into memslot0.
+	 */
+	nr_pages = 512;
+
+	/* Account for the per-vCPU stacks on behalf of the test. */
 	nr_pages += nr_runnable_vcpus * DEFAULT_STACK_PGS;
 
 	/*