KVM: selftests: page_table_test: fix calculation of guest_test_phys_mem

A kvm_page_table_test run with its default settings fails on VMX due to
memory region add failure:
> ==== Test Assertion Failure ====
>  lib/kvm_util.c:952: ret == 0
>  pid=10538 tid=10538 errno=17 - File exists
>     1  0x00000000004057d1: vm_userspace_mem_region_add at kvm_util.c:947
>     2  0x0000000000401ee9: pre_init_before_test at kvm_page_table_test.c:302
>     3   (inlined by) run_test at kvm_page_table_test.c:374
>     4  0x0000000000409754: for_each_guest_mode at guest_modes.c:53
>     5  0x0000000000401860: main at kvm_page_table_test.c:500
>     6  0x00007f82ae2d8554: ?? ??:0
>     7  0x0000000000401894: _start at ??:?
>  KVM_SET_USER_MEMORY_REGION IOCTL failed,
>  rc: -1 errno: 17
>  slot: 1 flags: 0x0
>  guest_phys_addr: 0xc0000000 size: 0x40000000

This is because the memory range that this test is trying to add
(0x0c0000000 - 0x100000000) conflicts with LAPIC mapping at 0x0fee00000.

Looking at the code it seems that guest_test_*phys*_mem variable gets
mistakenly overwritten with guest_test_*virt*_mem while trying to adjust
the former for alignment.
With the correct variable adjusted this test runs successfully.
Signed-off-by: NMaciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <52e487458c3172923549bbcf9dfccfbe6faea60b.1637940473.git.maciej.szmigiero@oracle.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/kvm_page_table_test.c

@@ -280,7 +280,7 @@ static struct kvm_vm *pre_init_before_test(enum vm_guest_mode mode, void *arg)
 #ifdef __s390x__
 	alignment = max(0x100000, alignment);
 #endif
-	guest_test_phys_mem = align_down(guest_test_virt_mem, alignment);
+	guest_test_phys_mem = align_down(guest_test_phys_mem, alignment);
 
 	/* Set up the shared data structure test_args */
 	test_args.vm = vm;