[PATCH RFC 0/2] Make fsgsbase test more stable

[PATCH RFC 0/2] Make fsgsbase test more stable

[Mark Brown]

This series attempts to make the fsgsbase test in the x86 kselftest
report a stable result.  On some Intel systems there are intermittent
failures in this testcase which have been reported and discussed 
previously:

   https://lore.kernel.org/lkml/20180126153631.ha7yc33fj5uhitjo@xps/

with the analysis concluding that this is a hardware issue affecting a
subset of systems but no fix has been merged as yet.  In order to at
least make the test more solid for use in automated testing this series
modifies it to execute the test often enough to reproduce the problem
reliably.

I'm not happy with this since it doesn't fix the actual problem, the
code isn't particularly clean and it makes the execution time for the
selftests much longer - my main goal here is to restart the discussion
of the test failure, I don't think merging this is a great idea.

Mark Brown (2):
      selftests/x86/fsgsbase: Indirect output through a wrapper function
      selftests/x86/fsgsbase: Default to trying to run the test repeatedly

 tools/testing/selftests/x86/fsgsbase.c | 79 +++++++++++++++++++++++++---------
 1 file changed, 58 insertions(+), 21 deletions(-)

[PATCH RFC 1/2] selftests/x86/fsgsbase: Indirect output through a wrapper function

[Mark Brown]

In preparation for a change to make this test run repeatedly which
would generate huge amounts of output as is indirect all the printf()
calls in the program through a wrapper and add a quiet flag which can
be used to suppress the output.  This is fairly quick and dirty, I'm not
100% sure what would be idiomatic here.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/x86/fsgsbase.c | 52 ++++++++++++++++----------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index f249e042b3b5..6cda6daa1f8c 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -7,6 +7,7 @@
 #define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdarg.h>
 #include <stdbool.h>
 #include <string.h>
 #include <sys/syscall.h>
@@ -32,6 +33,17 @@ static volatile sig_atomic_t want_segv;
 static volatile unsigned long segv_addr;
 
 static int nerrs;
+static bool quiet;
+
+static void logger(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	if (!quiet)
+		vprintf(fmt, args);
+	va_end(args);
+}
 
 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 		       int flags)
@@ -118,29 +130,29 @@ static void check_gs_value(unsigned long value)
 	unsigned long base;
 	unsigned short sel;
 
-	printf("[RUN]\tARCH_SET_GS to 0x%lx\n", value);
+	logger("[RUN]\tARCH_SET_GS to 0x%lx\n", value);
 	if (syscall(SYS_arch_prctl, ARCH_SET_GS, value) != 0)
 		err(1, "ARCH_SET_GS");
 
 	asm volatile ("mov %%gs, %0" : "=rm" (sel));
 	base = read_base(GS);
 	if (base == value) {
-		printf("[OK]\tGSBASE was set as expected (selector 0x%hx)\n",
+		logger("[OK]\tGSBASE was set as expected (selector 0x%hx)\n",
 		       sel);
 	} else {
 		nerrs++;
-		printf("[FAIL]\tGSBASE was not as expected: got 0x%lx (selector 0x%hx)\n",
+		logger("[FAIL]\tGSBASE was not as expected: got 0x%lx (selector 0x%hx)\n",
 		       base, sel);
 	}
 
 	if (syscall(SYS_arch_prctl, ARCH_GET_GS, &base) != 0)
 		err(1, "ARCH_GET_GS");
 	if (base == value) {
-		printf("[OK]\tARCH_GET_GS worked as expected (selector 0x%hx)\n",
+		logger("[OK]\tARCH_GET_GS worked as expected (selector 0x%hx)\n",
 		       sel);
 	} else {
 		nerrs++;
-		printf("[FAIL]\tARCH_GET_GS was not as expected: got 0x%lx (selector 0x%hx)\n",
+		logger("[FAIL]\tARCH_GET_GS was not as expected: got 0x%lx (selector 0x%hx)\n",
 		       base, sel);
 	}
 }
@@ -149,7 +161,7 @@ static void mov_0_gs(unsigned long initial_base, bool schedule)
 {
 	unsigned long base, arch_base;
 
-	printf("[RUN]\tARCH_SET_GS to 0x%lx then mov 0 to %%gs%s\n", initial_base, schedule ? " and schedule " : "");
+	logger("[RUN]\tARCH_SET_GS to 0x%lx then mov 0 to %%gs%s\n", initial_base, schedule ? " and schedule " : "");
 	if (syscall(SYS_arch_prctl, ARCH_SET_GS, initial_base) != 0)
 		err(1, "ARCH_SET_GS");
 
@@ -161,10 +173,10 @@ static void mov_0_gs(unsigned long initial_base, bool schedule)
 	if (syscall(SYS_arch_prctl, ARCH_GET_GS, &arch_base) != 0)
 		err(1, "ARCH_GET_GS");
 	if (base == arch_base) {
-		printf("[OK]\tGSBASE is 0x%lx\n", base);
+		logger("[OK]\tGSBASE is 0x%lx\n", base);
 	} else {
 		nerrs++;
-		printf("[FAIL]\tGSBASE changed to 0x%lx but kernel reports 0x%lx\n", base, arch_base);
+		logger("[FAIL]\tGSBASE changed to 0x%lx but kernel reports 0x%lx\n", base, arch_base);
 	}
 }
 
@@ -195,7 +207,7 @@ static void do_remote_base()
 
 	unsigned short sel;
 	asm volatile ("mov %%gs, %0" : "=rm" (sel));
-	printf("\tother thread: ARCH_SET_GS(0x%lx)%s -- sel is 0x%hx\n",
+	logger("\tother thread: ARCH_SET_GS(0x%lx)%s -- sel is 0x%hx\n",
 	       to_set, hard_zero ? " and clear gs" : "", sel);
 }
 
@@ -228,7 +240,7 @@ void do_unexpected_base(void)
 		.useable         = 0
 	};
 	if (syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)) == 0) {
-		printf("\tother thread: using LDT slot 0\n");
+		logger("\tother thread: using LDT slot 0\n");
 		asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)0x7));
 	} else {
 		/* No modify_ldt for us (configured out, perhaps) */
@@ -250,10 +262,10 @@ void do_unexpected_base(void)
 		munmap(low_desc, sizeof(desc));
 
 		if (ret != 0) {
-			printf("[NOTE]\tcould not create a segment -- test won't do anything\n");
+			logger("[NOTE]\tcould not create a segment -- test won't do anything\n");
 			return;
 		}
-		printf("\tother thread: using GDT slot %d\n", desc.entry_number);
+		logger("\tother thread: using GDT slot %d\n", desc.entry_number);
 		asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)((desc.entry_number << 3) | 0x3)));
 	}
 
@@ -298,10 +310,10 @@ static void set_gs_and_switch_to(unsigned long local,
 		local = 0;
 	}
 
-	printf("[RUN]\tARCH_SET_GS(0x%lx)%s, then schedule to 0x%lx\n",
+	logger("[RUN]\tARCH_SET_GS(0x%lx)%s, then schedule to 0x%lx\n",
 	       local, hard_zero ? " and clear gs" : "", remote);
 	if (force_sel)
-		printf("\tBefore schedule, set selector to 0x%hx\n", force_sel);
+		logger("\tBefore schedule, set selector to 0x%hx\n", force_sel);
 	if (syscall(SYS_arch_prctl, ARCH_SET_GS, local) != 0)
 		err(1, "ARCH_SET_GS");
 	if (hard_zero)
@@ -309,7 +321,7 @@ static void set_gs_and_switch_to(unsigned long local,
 
 	if (read_base(GS) != local) {
 		nerrs++;
-		printf("[FAIL]\tGSBASE wasn't set as expected\n");
+		logger("[FAIL]\tGSBASE wasn't set as expected\n");
 	}
 
 	if (force_sel) {
@@ -335,11 +347,11 @@ static void set_gs_and_switch_to(unsigned long local,
 	asm volatile ("mov %%gs, %0" : "=rm" (sel_post_sched));
 	base = read_base(GS);
 	if (base == local && sel_pre_sched == sel_post_sched) {
-		printf("[OK]\tGS/BASE remained 0x%hx/0x%lx\n",
+		logger("[OK]\tGS/BASE remained 0x%hx/0x%lx\n",
 		       sel_pre_sched, local);
 	} else {
 		nerrs++;
-		printf("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n",
+		logger("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n",
 		       sel_pre_sched, local, sel_post_sched, base);
 	}
 }
@@ -348,7 +360,7 @@ static void test_unexpected_base(void)
 {
 	unsigned long base;
 
-	printf("[RUN]\tARCH_SET_GS(0), clear gs, then manipulate GSBASE in a different thread\n");
+	logger("[RUN]\tARCH_SET_GS(0), clear gs, then manipulate GSBASE in a different thread\n");
 	if (syscall(SYS_arch_prctl, ARCH_SET_GS, 0) != 0)
 		err(1, "ARCH_SET_GS");
 	asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)0));
@@ -360,10 +372,10 @@ static void test_unexpected_base(void)
 
 	base = read_base(GS);
 	if (base == 0) {
-		printf("[OK]\tGSBASE remained 0\n");
+		logger("[OK]\tGSBASE remained 0\n");
 	} else {
 		nerrs++;
-		printf("[FAIL]\tGSBASE changed to 0x%lx\n", base);
+		logger("[FAIL]\tGSBASE changed to 0x%lx\n", base);
 	}
 }
 
-- 
2.19.1

[PATCH RFC 2/2] selftests/x86/fsgsbase: Default to trying to run the test repeatedly

[Mark Brown]

In automated testing it has been found that on many systems the fsgsbase
test fails intermittently.  This was reported and discussed a while
back:

    https://lore.kernel.org/lkml/20180126153631.ha7yc33fj5uhitjo@xps/

with the analysis concluding that this is a hardware issue affecting a
subset of systems but no fix has been merged as yet.  As well as the
actual problem found by testing the intermittent test failure is causing
issues for the people doing the automated testing due to the noise.

In order to make the testing stable modify the test program to iterate
through the test repeatedly, choosing 5000 iterations based on prior
reports and local testing.  This unfortunately greatly increases the
execution time for the selftests when things succeed which isn't great,
in my local tests on a range of systems it pushes the execution time up
to approximately a minute when no failures are encountered.

Reported-by: Dan Rue <dan.rue@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/x86/fsgsbase.c | 27 +++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 6cda6daa1f8c..83410749ff1f 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -379,7 +379,7 @@ static void test_unexpected_base(void)
 	}
 }
 
-int main()
+int test()
 {
 	pthread_t thread;
 
@@ -437,3 +437,28 @@ int main()
 
 	return nerrs == 0 ? 0 : 1;
 }
+
+int main()
+{
+	int tries = 5000;
+	int i;
+
+	if (tries > 1)
+		quiet = true;
+
+	for (i = 0; i < tries; i++) {
+		if (test() != 0)
+			break;
+	}
+
+	if (quiet) {
+		if (nerrs) {
+			printf("[FAIL] %d errors detected in %d tries\n",
+				nerrs, i + 1);
+		} else {
+			printf("[PASS] %d runs succeeded\n", i);
+		}
+	}
+
+	return nerrs == 0 ? 0 : 1;
+}
-- 
2.19.1