[tip:x86/urgent] selftests/x86: Disable the ldt_gdt_64 test for now

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  0f672809f91abd0aee01624ccad9199a62e3da7a
Gitweb:     http://git.kernel.org/tip/0f672809f91abd0aee01624ccad9199a62e3da7a
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Mon, 11 Jan 2016 17:23:32 -0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 12 Jan 2016 11:09:26 +0100

selftests/x86: Disable the ldt_gdt_64 test for now

ldt_gdt.c relies on cross-cpu invalidation of SS to do one of
its tests.  On 32-bit builds, this works fine, but on 64-bit
builds, it only works if the kernel has proper SS sigcontext
handling for 64-bit user programs.

Since the SS fixes are currently reverted, restrict the test
case to 32 bits for now.

In principle, I could change the test to use a different segment
register, but it would be messy: CS can't point to the LDT for
64-bit code, and the other registers don't result in immediate
faults because they aren't reloaded on kernel -> user
transitions.

When we fix sigcontext (in 4.6?), we can revert this.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/231591d9122d282402d8f53175134f8db5b3bc73.1452561752.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 tools/testing/selftests/x86/Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index eabcff4..398bb0e 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -4,9 +4,10 @@ include ../lib.mk
 
 .PHONY: all all_32 all_64 warn_32bit_failure clean
 
-TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt syscall_nt ptrace_syscall
+TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall
 TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault sigreturn test_syscall_vdso unwind_vdso \
-			test_FCMOV test_FCOMI test_FISTTP
+			test_FCMOV test_FCOMI test_FISTTP \
+			ldt_gdt
 
 TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
 BINARIES_32 := $(TARGETS_C_32BIT_ALL:%=%_32)