selftests/x86/ldt_get: Add a few additional tests for limits

We weren't testing the .limit and .limit_in_pages fields very well.
Add more tests.

This addition seems to trigger the "bits 16:19 are undefined" issue
that was fixed in an earlier patch.  I think that, at least on my
CPU, the high nibble of the limit ends in LAR bits 16:19.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/5601c15ea9b3113d288953fd2838b18bedf6bc67.1509794321.git.luto@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

tools/testing/selftests/x86/ldt_gdt.c

@@ -404,9 +404,24 @@ static void do_simple_tests(void)
 	install_invalid(&desc, false);
 
 	desc.seg_not_present = 0;
-	desc.read_exec_only = 0;
 	desc.seg_32bit = 1;
+	desc.read_exec_only = 0;
+	desc.limit = 0xfffff;
+
 	install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB);
+
+	desc.limit_in_pages = 1;
+
+	install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB | AR_G);
+	desc.read_exec_only = 1;
+	install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S | AR_P | AR_DB | AR_G);
+	desc.contents = 1;
+	desc.read_exec_only = 0;
+	install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA_EXPDOWN | AR_S | AR_P | AR_DB | AR_G);
+	desc.read_exec_only = 1;
+	install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA_EXPDOWN | AR_S | AR_P | AR_DB | AR_G);
+
+	desc.limit = 0;
 	install_invalid(&desc, true);
 }