[PATCH v2] selftests/x86: Disable ldt_gdt_64 for now

From: Andy Lutomirski
Date: Mon Jan 11 2016 - 20:23:41 EST

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@xxxxxxxxxx>

Changes from v1: based on tip:x86/asm

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 eabcff411984..398bb0e6e38c 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

BINARIES_32 := $(TARGETS_C_32BIT_ALL:%=%_32)