KVM: selftests: Ignore KVM 5-level paging support for VM_MODE_PXXV48_4K

Explicitly set the VA width to 48 bits for the x86_64-only PXXV48_4K VM
mode instead of asserting the guest VA width is 48 bits.  The fact that
KVM supports 5-level paging is irrelevant unless the selftests opt-in to
5-level paging by setting CR4.LA57 for the guest.  The overzealous
assert prevents running the selftests on a kernel with 5-level paging
enabled.

Incorporate LA57 into the assert instead of removing the assert entirely
as a sanity check of KVM's CPUID output.

Fixes: 567a9f1e ("KVM: selftests: Introduce VM_MODE_PXXV48_4K")
Reported-by: Sergio Perez Gonzalez <sergio.perez.gonzalez@intel.com>
Cc: Adriana Cervantes Jimenez <adriana.cervantes.jimenez@intel.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200528021530.28091-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -195,11 +195,18 @@ struct kvm_vm *_vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm)
 	case VM_MODE_PXXV48_4K:
 #ifdef __x86_64__
 		kvm_get_cpu_address_width(&vm->pa_bits, &vm->va_bits);
-		TEST_ASSERT(vm->va_bits == 48, "Linear address width "
-			    "(%d bits) not supported", vm->va_bits);
+		/*
+		 * Ignore KVM support for 5-level paging (vm->va_bits == 57),
+		 * it doesn't take effect unless a CR4.LA57 is set, which it
+		 * isn't for this VM_MODE.
+		 */
+		TEST_ASSERT(vm->va_bits == 48 || vm->va_bits == 57,
+			    "Linear address width (%d bits) not supported",
+			    vm->va_bits);
 		pr_debug("Guest physical address width detected: %d\n",
 			 vm->pa_bits);
 		vm->pgtable_levels = 4;
+		vm->va_bits = 48;
 #else
 		TEST_FAIL("VM_MODE_PXXV48_4K not supported on non-x86 platforms");
 #endif