[PATCH 0/2] perf tests: Check for ARM [vectors] page

[PATCH 0/2] perf tests: Check for ARM [vectors] page

[Florian Fainelli]

Hi all,

I just painfully learned that perf would segfault when
CONFIG_KUSER_HELPERS is disabled because it unconditionally makes use of
it. This patch series adds an ARM test for that by leveraging the
existing find_vdso_map() function and making it more generic and capable
of location any map within /proc/self/maps.

Florian Fainelli (2):
  perf tools: Make find_vdso_map() more modular
  perf tests: Add a test for the ARM 32-bit [vectors] page

 tools/perf/arch/arm/tests/Build          |  1 +
 tools/perf/arch/arm/tests/arch-tests.c   |  4 +++
 tools/perf/arch/arm/tests/vectors-page.c | 20 +++++++++++++++
 tools/perf/tests/tests.h                 |  5 ++++
 tools/perf/util/find-map.c               | 31 ++++++++++++++++++++++++
 tools/perf/util/find-vdso-map.c          | 30 +++--------------------
 6 files changed, 64 insertions(+), 27 deletions(-)
 create mode 100644 tools/perf/arch/arm/tests/vectors-page.c
 create mode 100644 tools/perf/util/find-map.c

-- 
2.17.1

[PATCH 1/2] perf tools: Make find_vdso_map() more modular

[Florian Fainelli]

In preparation for checking that the vectors page on the ARM
architecture, refactor the find_vdso_map() function to accept finding an
arbitrary string and create a dedicated helper function for that under
util/find-map.c and update find_vdso_map() to use it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 tools/perf/util/find-map.c      | 31 +++++++++++++++++++++++++++++++
 tools/perf/util/find-vdso-map.c | 30 +++---------------------------
 2 files changed, 34 insertions(+), 27 deletions(-)
 create mode 100644 tools/perf/util/find-map.c

diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
new file mode 100644
index 000000000000..42533fc21108
--- /dev/null
+++ b/tools/perf/util/find-map.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+static int find_map(void **start, void **end, const char *name)
+{
+	FILE *maps;
+	char line[128];
+	int found = 0;
+
+	maps = fopen("/proc/self/maps", "r");
+	if (!maps) {
+		fprintf(stderr, "vdso: cannot open maps\n");
+		return -1;
+	}
+
+	while (!found && fgets(line, sizeof(line), maps)) {
+		int m = -1;
+
+		/* We care only about private r-x mappings. */
+		if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
+				start, end, &m))
+			continue;
+		if (m < 0)
+			continue;
+
+		if (!strncmp(&line[m], name, sizeof(name) - 1))
+			found = 1;
+	}
+
+	fclose(maps);
+	return !found;
+}
+
diff --git a/tools/perf/util/find-vdso-map.c b/tools/perf/util/find-vdso-map.c
index d7823e3508fc..840d7d6e29e2 100644
--- a/tools/perf/util/find-vdso-map.c
+++ b/tools/perf/util/find-vdso-map.c
@@ -1,31 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
+#include "find-map.c"
+
 static int find_vdso_map(void **start, void **end)
 {
-	FILE *maps;
-	char line[128];
-	int found = 0;
-
-	maps = fopen("/proc/self/maps", "r");
-	if (!maps) {
-		fprintf(stderr, "vdso: cannot open maps\n");
-		return -1;
-	}
-
-	while (!found && fgets(line, sizeof(line), maps)) {
-		int m = -1;
-
-		/* We care only about private r-x mappings. */
-		if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
-				start, end, &m))
-			continue;
-		if (m < 0)
-			continue;
-
-		if (!strncmp(&line[m], VDSO__MAP_NAME,
-			     sizeof(VDSO__MAP_NAME) - 1))
-			found = 1;
-	}
-
-	fclose(maps);
-	return !found;
+	return find_map(start, end, VDSO__MAP_NAME);
 }
-- 
2.17.1

Re: [PATCH 1/2] perf tools: Make find_vdso_map() more modular

[Florian Fainelli]

On 10/24/18 5:09 PM, Florian Fainelli wrote:
> In preparation for checking that the vectors page on the ARM
> architecture, refactor the find_vdso_map() function to accept finding an
> arbitrary string and create a dedicated helper function for that under
> util/find-map.c and update find_vdso_map() to use it.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  tools/perf/util/find-map.c      | 31 +++++++++++++++++++++++++++++++
>  tools/perf/util/find-vdso-map.c | 30 +++---------------------------
>  2 files changed, 34 insertions(+), 27 deletions(-)
>  create mode 100644 tools/perf/util/find-map.c
> 
> diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
> new file mode 100644
> index 000000000000..42533fc21108
> --- /dev/null
> +++ b/tools/perf/util/find-map.c
> @@ -0,0 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0
> +static int find_map(void **start, void **end, const char *name)
> +{
> +	FILE *maps;
> +	char line[128];
> +	int found = 0;
> +
> +	maps = fopen("/proc/self/maps", "r");
> +	if (!maps) {
> +		fprintf(stderr, "vdso: cannot open maps\n");
> +		return -1;
> +	}
> +
> +	while (!found && fgets(line, sizeof(line), maps)) {
> +		int m = -1;
> +
> +		/* We care only about private r-x mappings. */
> +		if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
> +				start, end, &m))
> +			continue;
> +		if (m < 0)
> +			continue;
> +
> +		if (!strncmp(&line[m], name, sizeof(name) - 1))

Meh, this should be strlen() now, but I would like to hear comments
before submitting a v2 of this anyway. Thanks!
-- 
Florian

[PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Florian Fainelli]

perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
independance with respect to the ARM CPU being used. Add a test which
tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
turned on to help asses the system's health.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 tools/perf/arch/arm/tests/Build          |  1 +
 tools/perf/arch/arm/tests/arch-tests.c   |  4 ++++
 tools/perf/arch/arm/tests/vectors-page.c | 20 ++++++++++++++++++++
 tools/perf/tests/tests.h                 |  5 +++++
 4 files changed, 30 insertions(+)
 create mode 100644 tools/perf/arch/arm/tests/vectors-page.c

diff --git a/tools/perf/arch/arm/tests/Build b/tools/perf/arch/arm/tests/Build
index 883c57ff0c08..d9ae2733f9cc 100644
--- a/tools/perf/arch/arm/tests/Build
+++ b/tools/perf/arch/arm/tests/Build
@@ -1,4 +1,5 @@
 libperf-y += regs_load.o
 libperf-y += dwarf-unwind.o
+libperf-y += vectors-page.o
 
 libperf-y += arch-tests.o
diff --git a/tools/perf/arch/arm/tests/arch-tests.c b/tools/perf/arch/arm/tests/arch-tests.c
index 5b1543c98022..6848101a855f 100644
--- a/tools/perf/arch/arm/tests/arch-tests.c
+++ b/tools/perf/arch/arm/tests/arch-tests.c
@@ -10,6 +10,10 @@ struct test arch_tests[] = {
 		.func = test__dwarf_unwind,
 	},
 #endif
+	{
+		.desc = "Vectors page",
+		.func = test__vectors_page,
+	},
 	{
 		.func = NULL,
 	},
diff --git a/tools/perf/arch/arm/tests/vectors-page.c b/tools/perf/arch/arm/tests/vectors-page.c
new file mode 100644
index 000000000000..e44223cbf0df
--- /dev/null
+++ b/tools/perf/arch/arm/tests/vectors-page.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <string.h>
+#include <linux/compiler.h>
+
+#include "tests/tests.h"
+#include "util/find-map.c"
+
+#define VECTORS__MAP_NAME "[vectors]"
+
+int test__vectors_page(struct test *test __maybe_unused,
+		       int subtest __maybe_unused)
+{
+	void *start, *end;
+
+	if (find_map(&start, &end, VECTORS__MAP_NAME))
+		return -1;
+
+	return 0;
+}
diff --git a/tools/perf/tests/tests.h b/tools/perf/tests/tests.h
index b82f55fcc294..399f18ca71a3 100644
--- a/tools/perf/tests/tests.h
+++ b/tools/perf/tests/tests.h
@@ -119,4 +119,9 @@ int test__arch_unwind_sample(struct perf_sample *sample,
 			     struct thread *thread);
 #endif
 #endif
+
+#if defined(__arm__)
+int test__vectors_page(struct test *test, int subtest);
+#endif
+
 #endif /* TESTS_H */
-- 
2.17.1

Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Andrew Lunn]

On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
> independance with respect to the ARM CPU being used. Add a test which
> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
> turned on to help asses the system's health.

Hi Florian

I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
segfaults give little clue as to what is going wrong,and gdb is not
much use either.

What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
ARM?

	Andrew

Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Florian Fainelli]

On 10/24/18 7:10 PM, Andrew Lunn wrote:
> On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
>> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
>> independance with respect to the ARM CPU being used. Add a test which
>> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
>> turned on to help asses the system's health.
> 
> Hi Florian
> 
> I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
> segfaults give little clue as to what is going wrong,and gdb is not
> much use either.

If you have a working backtrace, you can typically see the virtual
address being in 0xffff_xxxx which gives a bit of a clue, but yes, this
is not particularly helpful.

> 
> What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
> fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
> ARM?

Sure, sounds reasonable, thanks for taking a look.
-- 
Florian

Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Russell King - ARM Linux]

On Thu, Oct 25, 2018 at 10:19:54AM -0700, Florian Fainelli wrote:
> On 10/24/18 7:10 PM, Andrew Lunn wrote:
> > On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
> >> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
> >> independance with respect to the ARM CPU being used. Add a test which
> >> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
> >> turned on to help asses the system's health.
> > 
> > Hi Florian
> > 
> > I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
> > segfaults give little clue as to what is going wrong,and gdb is not
> > much use either.
> 
> If you have a working backtrace, you can typically see the virtual
> address being in 0xffff_xxxx which gives a bit of a clue, but yes, this
> is not particularly helpful.
> 
> > 
> > What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
> > fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
> > ARM?
> 
> Sure, sounds reasonable, thanks for taking a look.

An alternative would be rather than adding this to user programs, to
have the kernel detect it and print a warning itself.

BTW, I note that the help text for CONFIG_KUSER_HELPERS needs to be
updated.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Florian Fainelli]

On 10/25/18 10:32 AM, Russell King - ARM Linux wrote:
> On Thu, Oct 25, 2018 at 10:19:54AM -0700, Florian Fainelli wrote:
>> On 10/24/18 7:10 PM, Andrew Lunn wrote:
>>> On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
>>>> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
>>>> independance with respect to the ARM CPU being used. Add a test which
>>>> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
>>>> turned on to help asses the system's health.
>>>
>>> Hi Florian
>>>
>>> I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
>>> segfaults give little clue as to what is going wrong,and gdb is not
>>> much use either.
>>
>> If you have a working backtrace, you can typically see the virtual
>> address being in 0xffff_xxxx which gives a bit of a clue, but yes, this
>> is not particularly helpful.
>>
>>>
>>> What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
>>> fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
>>> ARM?
>>
>> Sure, sounds reasonable, thanks for taking a look.
> 
> An alternative would be rather than adding this to user programs, to
> have the kernel detect it and print a warning itself.

Something like this below? It does not have to be an alternative
solution, I would find it useful for perf to make sure the vectors page
is present in the virtual address space by having an explicit test. perf
maintains, what do you think?

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index f4ea4c62c613..b045b48d368d 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned
long addr,
                show_regs(regs);
        }
 #endif
+#ifndef CONFIG_KUSER_HELPERS
+       if (((addr & PAGE_MASK) == 0xffff0000) && (sig == SIGSEGV))
+               printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at
0x%08lx\n",
+                      tsk->comm, addr);
+#endif

        tsk->thread.address = addr;
        tsk->thread.error_code = fsr;


> 
> BTW, I note that the help text for CONFIG_KUSER_HELPERS needs to be
> updated.
> 


-- 
Florian

Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

[Russell King - ARM Linux]

On Thu, Oct 25, 2018 at 10:53:12AM -0700, Florian Fainelli wrote:
> Something like this below? It does not have to be an alternative
> solution, I would find it useful for perf to make sure the vectors page
> is present in the virtual address space by having an explicit test. perf
> maintains, what do you think?

Yep, I'd swap the two tests merely because the check for 'sig' will be
slightly cheaper than the mask-and-test of addr, but it probably doesn't
make that much difference.

> 
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index f4ea4c62c613..b045b48d368d 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned
> long addr,
>                 show_regs(regs);
>         }
>  #endif
> +#ifndef CONFIG_KUSER_HELPERS
> +       if (((addr & PAGE_MASK) == 0xffff0000) && (sig == SIGSEGV))
> +               printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at
> 0x%08lx\n",
> +                      tsk->comm, addr);
> +#endif
> 
>         tsk->thread.address = addr;
>         tsk->thread.error_code = fsr;
> 
> 
> > 
> > BTW, I note that the help text for CONFIG_KUSER_HELPERS needs to be
> > updated.
> > 
> 
> 
> -- 
> Florian

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

Re: [PATCH 0/2] perf tests: Check for ARM [vectors] page

[Florian Fainelli]

On 10/24/18 5:09 PM, Florian Fainelli wrote:
> Hi all,
> 
> I just painfully learned that perf would segfault when
> CONFIG_KUSER_HELPERS is disabled because it unconditionally makes use of
> it. This patch series adds an ARM test for that by leveraging the
> existing find_vdso_map() function and making it more generic and capable
> of location any map within /proc/self/maps.

Any feedback on this?

> 
> Florian Fainelli (2):
>   perf tools: Make find_vdso_map() more modular
>   perf tests: Add a test for the ARM 32-bit [vectors] page
> 
>  tools/perf/arch/arm/tests/Build          |  1 +
>  tools/perf/arch/arm/tests/arch-tests.c   |  4 +++
>  tools/perf/arch/arm/tests/vectors-page.c | 20 +++++++++++++++
>  tools/perf/tests/tests.h                 |  5 ++++
>  tools/perf/util/find-map.c               | 31 ++++++++++++++++++++++++
>  tools/perf/util/find-vdso-map.c          | 30 +++--------------------
>  6 files changed, 64 insertions(+), 27 deletions(-)
>  create mode 100644 tools/perf/arch/arm/tests/vectors-page.c
>  create mode 100644 tools/perf/util/find-map.c
> 


-- 
Florian