[PATCH v3 0/2] Base enablement of IOMMU debugfs support

[PATCH v3 0/2] Base enablement of IOMMU debugfs support

[Gary R Hook]

These patches create a top-level function to create a debugfs directory
for the IOMMU, under which drivers may create and populate-specific
directories for their device internals.

Patch 1: general IOMMU enablement
Patch 2: basic AMD enablement to demonstrate linkage with patch 1

Introduce a new Kconfig parameter IOMMU_DEBUG to globally allow or
disallow debugfs code to be built.

Changes since v2:
 - Move a declaration to outside an ifdef
 - Remove a spurious blank line

Changes since v1:
 - Remove debug cruft
 - Remove cruft produced by design change
 - Change the lock to a mutex
 - Coding style fixes
 - Add a comment to document the framework

---

Gary R Hook (2):
      iommu - Enable debugfs exposure of the IOMMU
      iommu/amd: Add basic debugfs infrastructure for AMD IOMMU


 drivers/iommu/Kconfig             |   11 +++++++
 drivers/iommu/Makefile            |    2 +
 drivers/iommu/amd_iommu_debugfs.c |   45 +++++++++++++++++++++++++++++
 drivers/iommu/amd_iommu_init.c    |    6 +++-
 drivers/iommu/amd_iommu_proto.h   |    6 ++++
 drivers/iommu/amd_iommu_types.h   |    3 ++
 drivers/iommu/iommu-debugfs.c     |   58 +++++++++++++++++++++++++++++++++++++
 include/linux/iommu.h             |    4 +++
 8 files changed, 133 insertions(+), 2 deletions(-)
 create mode 100644 drivers/iommu/amd_iommu_debugfs.c
 create mode 100644 drivers/iommu/iommu-debugfs.c

--
Effective helpfulness requires thoroughness

[PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Gary R Hook]

Provide base enablement for using debugfs to expose internal data of
an IOMMU driver. When called, create the /sys/kernel/debug/iommu
directory.  Emit a strong warning at boot time to indicate that this
feature is enabled.

This patch adds a top-level function that will create the (above)
directory, under which a driver may create a hw-specific directory for
its use. The function

	iommu_debugfs_setup()

returns a pointer to the new dentry structure created for
/sys/kernel/debug/iommu, or NULL in the event of a failure. An IOMMU
driver should call this function first, and then create a directory
beneath it. A driver implementation might look something like:

static struct dentry *my_debugfs;

	struct dentry *d_top;
	if (!my_debugfs) {
		d_top = iommu_debugfs_setup();
		if (d_top)
			my_debugfs = debugfs_create_dir("vendor", d_top);
	}

Since the IOMMU driver can not be removed from the running system, this
patch only provides an "on" function.

Signed-off-by: Gary R Hook <gary.hook-5C7GfCeVMHo@public.gmane.org>
---
 drivers/iommu/Kconfig         |   11 ++++++++
 drivers/iommu/Makefile        |    1 +
 drivers/iommu/iommu-debugfs.c |   58 +++++++++++++++++++++++++++++++++++++++++
 include/linux/iommu.h         |    4 +++
 4 files changed, 74 insertions(+)
 create mode 100644 drivers/iommu/iommu-debugfs.c

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index f3a21343e636..c1e39dabfec2 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
 
 endmenu
 
+config IOMMU_DEBUG
+	bool "Enable IOMMU internals in DebugFS"
+	depends on DEBUG_FS
+	default n
+	help
+	  Allows exposure of IOMMU device internals. This option enables
+	  the use of debugfs by IOMMU drivers as required. Devices can,
+	  at initialization time, cause the IOMMU code to create a top-level
+	  debug/iommu directory, and then populate a subdirectory with
+	  entries as required.
+
 config IOMMU_IOVA
 	tristate
 
diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index 1fb695854809..5eb1121d54b9 100644
--- a/drivers/iommu/Makefile
+++ b/drivers/iommu/Makefile
@@ -2,6 +2,7 @@
 obj-$(CONFIG_IOMMU_API) += iommu.o
 obj-$(CONFIG_IOMMU_API) += iommu-traces.o
 obj-$(CONFIG_IOMMU_API) += iommu-sysfs.o
+obj-$(CONFIG_IOMMU_DEBUG) += iommu-debugfs.o
 obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
 obj-$(CONFIG_IOMMU_IO_PGTABLE) += io-pgtable.o
 obj-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
diff --git a/drivers/iommu/iommu-debugfs.c b/drivers/iommu/iommu-debugfs.c
new file mode 100644
index 000000000000..add6f95120e4
--- /dev/null
+++ b/drivers/iommu/iommu-debugfs.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IOMMU driver
+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ *
+ * Author: Gary R Hook <gary.hook-5C7GfCeVMHo@public.gmane.org>
+ */
+
+#include <linux/pci.h>
+#include <linux/iommu.h>
+#include <linux/debugfs.h>
+
+static struct dentry *iommu_debugfs_dir;
+
+/*
+ * Provide base enablement for using debugfs to expose internal data of an
+ * IOMMU driver. When called, create the /sys/kernel/debug/iommu directory.
+ *
+ * Emit a strong warning at boot time to indicate that this feature is
+ * enabled.
+ *
+ * This top-level function that will create the (above) directory, under a
+ * driver may create a hw-specific directory for its use. The function
+ *
+ *     iommu_debugfs_setup()
+ *
+ * returns a pointer to the new dentry structure created for
+ * /sys/kernel/debug/iommu, or NULL in the event of a failure. An IOMMU
+ * driver should call this function first, and then create a directory
+ * beneath it. A driver implementation might look something like:
+ *
+ * static struct dentry *my_debugfs;
+ *
+ *    struct dentry *d_top;
+ *    if (!my_debugfs) {
+ *        d_top = iommu_debugfs_setup();
+ *        if (d_top)
+ *            my_debugfs = debugfs_create_dir("vendor", d_top);
+ *    }
+ *
+ * Since the IOMMU driver can not be removed from the running system, there
+ * is no need for an "off" function.
+ */
+struct dentry *iommu_debugfs_setup(void)
+{
+	if (!debugfs_initialized())
+		return NULL;
+
+	if (!iommu_debugfs_dir)
+		iommu_debugfs_dir = debugfs_create_dir("iommu", NULL);
+
+	if (iommu_debugfs_dir)
+		pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL\n");
+
+	return iommu_debugfs_dir;
+}
+EXPORT_SYMBOL_GPL(iommu_debugfs_setup);
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 19938ee6eb31..ccf7c1d800b0 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -698,4 +698,8 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
 
 #endif /* CONFIG_IOMMU_API */
 
+#ifdef CONFIG_IOMMU_DEBUG
+struct dentry *iommu_debugfs_setup(void);
+#endif
+
 #endif /* __LINUX_IOMMU_H */

Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Mehta, Sohil]

On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> 
> 
> +struct dentry *iommu_debugfs_setup(void)
> +{
> +	if (!debugfs_initialized())

This check is probably not needed.

> +		return NULL;
> +
> +	if (!iommu_debugfs_dir)
> +		iommu_debugfs_dir = debugfs_create_dir("iommu",
> NULL);
> +
> +	if (iommu_debugfs_dir)
> +		pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN
> ENABLED IN THIS KERNEL\n");
> +

As this gets called for each IOMMU, do you want to use pr_warn_once?

> +	return iommu_debugfs_dir;
> +}
> +EXPORT_SYMBOL_GPL(iommu_debugfs_setup);

-Sohil
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Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Hook, Gary]

On 4/13/2018 7:55 PM, Mehta, Sohil wrote:
> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>   
>>   
>> +struct dentry *iommu_debugfs_setup(void)
>> +{
>> +	if (!debugfs_initialized())
> 
> This check is probably not needed.

Ah, so it isn't. Thank you.

> 
>> +		return NULL;
>> +
>> +	if (!iommu_debugfs_dir)
>> +		iommu_debugfs_dir = debugfs_create_dir("iommu",
>> NULL);
>> +
>> +	if (iommu_debugfs_dir)
>> +		pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN
>> ENABLED IN THIS KERNEL\n");
>> +
> 
> As this gets called for each IOMMU, do you want to use pr_warn_once?

That works, yes.

> 
>> +	return iommu_debugfs_dir;
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_debugfs_setup);
> 
> -Sohil
> 

Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Robin Murphy]

On 17/04/18 18:36, Hook, Gary wrote:
> On 4/13/2018 7:55 PM, Mehta, Sohil wrote:
>> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>> +struct dentry *iommu_debugfs_setup(void)
>>> +{
>>> +    if (!debugfs_initialized())
>>
>> This check is probably not needed.
> 
> Ah, so it isn't. Thank you.
> 
>>
>>> +        return NULL;
>>> +
>>> +    if (!iommu_debugfs_dir)
>>> +        iommu_debugfs_dir = debugfs_create_dir("iommu",
>>> NULL);
>>> +
>>> +    if (iommu_debugfs_dir)
>>> +        pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN
>>> ENABLED IN THIS KERNEL\n");
>>> +
>>
>> As this gets called for each IOMMU, do you want to use pr_warn_once?
> 
> That works, yes.

Or I guess you could just roll the pr_warn() into the previous if() 
condition, i.e. only warn when the singleton debugfs_dir is actually 
created.

Robin.

> 
>>
>>> +    return iommu_debugfs_dir;
>>> +}
>>> +EXPORT_SYMBOL_GPL(iommu_debugfs_setup);
>>
>> -Sohil
>>
> 
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
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Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Hook, Gary]

On 4/17/2018 1:55 PM, Robin Murphy wrote:
> On 17/04/18 18:36, Hook, Gary wrote:
>> On 4/13/2018 7:55 PM, Mehta, Sohil wrote:
>>> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>>> +struct dentry *iommu_debugfs_setup(void)
>>>> +{
>>>> +    if (!debugfs_initialized())
>>>
>>> This check is probably not needed.
>>
>> Ah, so it isn't. Thank you.
>>
>>>
>>>> +        return NULL;
>>>> +
>>>> +    if (!iommu_debugfs_dir)
>>>> +        iommu_debugfs_dir = debugfs_create_dir("iommu",
>>>> NULL);
>>>> +
>>>> +    if (iommu_debugfs_dir)
>>>> +        pr_warn("WARNING: IOMMU DEBUGFS SUPPORT HAS BEEN
>>>> ENABLED IN THIS KERNEL\n");
>>>> +
>>>
>>> As this gets called for each IOMMU, do you want to use pr_warn_once?
>>
>> That works, yes.
> 
> Or I guess you could just roll the pr_warn() into the previous if() 
> condition, i.e. only warn when the singleton debugfs_dir is actually 
> created.

That makes more sense for a code path this isn't going to be hit more 
than a few times at most.

> 
> Robin.
> 
>>
>>>
>>>> +    return iommu_debugfs_dir;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(iommu_debugfs_setup);
>>>
>>> -Sohil
>>>
>>
>> _______________________________________________
>> iommu mailing list
>> iommu@lists.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/iommu

Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Hook, Gary]

On 4/6/2018 9:17 AM, Gary R Hook wrote:
> Provide base enablement for using debugfs to expose internal data of
> an IOMMU driver. When called, create the /sys/kernel/debug/iommu
> directory.  Emit a strong warning at boot time to indicate that this
> feature is enabled.
> 
> This patch adds a top-level function that will create the (above)
> directory, under which a driver may create a hw-specific directory for
> its use. The function
> 
> 	iommu_debugfs_setup()
> 
> returns a pointer to the new dentry structure created for
> /sys/kernel/debug/iommu, or NULL in the event of a failure. An IOMMU
> driver should call this function first, and then create a directory
> beneath it. A driver implementation might look something like:
> 
> static struct dentry *my_debugfs;
> 
> 	struct dentry *d_top;
> 	if (!my_debugfs) {
> 		d_top = iommu_debugfs_setup();
> 		if (d_top)
> 			my_debugfs = debugfs_create_dir("vendor", d_top);
> 	}
> 
> Since the IOMMU driver can not be removed from the running system, this
> patch only provides an "on" function.
> 
> Signed-off-by: Gary R Hook <gary.hook-5C7GfCeVMHo@public.gmane.org>
> ---
>   drivers/iommu/Kconfig         |   11 ++++++++
>   drivers/iommu/Makefile        |    1 +
>   drivers/iommu/iommu-debugfs.c |   58 +++++++++++++++++++++++++++++++++++++++++
>   include/linux/iommu.h         |    4 +++
>   4 files changed, 74 insertions(+)
>   create mode 100644 drivers/iommu/iommu-debugfs.c
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index f3a21343e636..c1e39dabfec2 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>   
>   endmenu
>   
> +config IOMMU_DEBUG
> +	bool "Enable IOMMU internals in DebugFS"
> +	depends on DEBUG_FS
> +	default n
> +	help
> +	  Allows exposure of IOMMU device internals. This option enables
> +	  the use of debugfs by IOMMU drivers as required. Devices can,
> +	  at initialization time, cause the IOMMU code to create a top-level
> +	  debug/iommu directory, and then populate a subdirectory with
> +	  entries as required.

I should explicitly ask about this:

Joerg had suggested IOMMU_DEBUGFS, but here I've changed to IOMMU_DEBUG. 
I'm not seeing a lot of CONFIG options that use DEBUGFS for debugfs 
options, so I chose to follow an implied convention.

Question: should this indeed be IOMMU_DEBUGFS?
                                 ^^^^^^^^^^^^^

Re: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU

[Robin Murphy]

On 17/04/18 18:46, Hook, Gary wrote:
> On 4/6/2018 9:17 AM, Gary R Hook wrote:
>> Provide base enablement for using debugfs to expose internal data of
>> an IOMMU driver. When called, create the /sys/kernel/debug/iommu
>> directory.  Emit a strong warning at boot time to indicate that this
>> feature is enabled.
>>
>> This patch adds a top-level function that will create the (above)
>> directory, under which a driver may create a hw-specific directory for
>> its use. The function
>>
>>     iommu_debugfs_setup()
>>
>> returns a pointer to the new dentry structure created for
>> /sys/kernel/debug/iommu, or NULL in the event of a failure. An IOMMU
>> driver should call this function first, and then create a directory
>> beneath it. A driver implementation might look something like:
>>
>> static struct dentry *my_debugfs;
>>
>>     struct dentry *d_top;
>>     if (!my_debugfs) {
>>         d_top = iommu_debugfs_setup();
>>         if (d_top)
>>             my_debugfs = debugfs_create_dir("vendor", d_top);
>>     }
>>
>> Since the IOMMU driver can not be removed from the running system, this
>> patch only provides an "on" function.
>>
>> Signed-off-by: Gary R Hook <gary.hook@amd.com>
>> ---
>>   drivers/iommu/Kconfig         |   11 ++++++++
>>   drivers/iommu/Makefile        |    1 +
>>   drivers/iommu/iommu-debugfs.c |   58 
>> +++++++++++++++++++++++++++++++++++++++++
>>   include/linux/iommu.h         |    4 +++
>>   4 files changed, 74 insertions(+)
>>   create mode 100644 drivers/iommu/iommu-debugfs.c
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index f3a21343e636..c1e39dabfec2 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>>   endmenu
>> +config IOMMU_DEBUG
>> +    bool "Enable IOMMU internals in DebugFS"
>> +    depends on DEBUG_FS
>> +    default n
>> +    help
>> +      Allows exposure of IOMMU device internals. This option enables
>> +      the use of debugfs by IOMMU drivers as required. Devices can,
>> +      at initialization time, cause the IOMMU code to create a top-level
>> +      debug/iommu directory, and then populate a subdirectory with
>> +      entries as required.
> 
> I should explicitly ask about this:
> 
> Joerg had suggested IOMMU_DEBUGFS, but here I've changed to IOMMU_DEBUG. 
> I'm not seeing a lot of CONFIG options that use DEBUGFS for debugfs 
> options, so I chose to follow an implied convention.
> 
> Question: should this indeed be IOMMU_DEBUGFS?
>                                  ^^^^^^^^^^^^^

Personally I'd say yes, since there is at least some precedent for 
*_DEBUGFS already, and it does help make the intent that much clearer 
(*_DEBUG often just means lots of dmesg spam rather than an actual 
debugfs interface).

Robin.
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[PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Gary R Hook]

Implement a skeleton framework for debugfs support in the
AMD IOMMU.


Signed-off-by: Gary R Hook <gary.hook-5C7GfCeVMHo@public.gmane.org>
---
 drivers/iommu/Makefile            |    1 +
 drivers/iommu/amd_iommu_debugfs.c |   45 +++++++++++++++++++++++++++++++++++++
 drivers/iommu/amd_iommu_init.c    |    6 +++--
 drivers/iommu/amd_iommu_proto.h   |    6 +++++
 drivers/iommu/amd_iommu_types.h   |    3 ++
 5 files changed, 59 insertions(+), 2 deletions(-)
 create mode 100644 drivers/iommu/amd_iommu_debugfs.c

diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index 5eb1121d54b9..0ca250f626d9 100644
--- a/drivers/iommu/Makefile
+++ b/drivers/iommu/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_IOMMU_IOVA) += iova.o
 obj-$(CONFIG_OF_IOMMU)	+= of_iommu.o
 obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
 obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o
+obj-$(CONFIG_IOMMU_DEBUG) += amd_iommu_debugfs.o
 obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
 obj-$(CONFIG_ARM_SMMU) += arm-smmu.o
 obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
diff --git a/drivers/iommu/amd_iommu_debugfs.c b/drivers/iommu/amd_iommu_debugfs.c
new file mode 100644
index 000000000000..282100a655b3
--- /dev/null
+++ b/drivers/iommu/amd_iommu_debugfs.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD IOMMU driver
+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ *
+ * Author: Gary R Hook <gary.hook-5C7GfCeVMHo@public.gmane.org>
+ */
+
+#include <linux/debugfs.h>
+#include <linux/iommu.h>
+#include <linux/pci.h>
+#include "amd_iommu_proto.h"
+#include "amd_iommu_types.h"
+
+static struct dentry *amd_iommu_debugfs;
+static DEFINE_MUTEX(amd_iommu_debugfs_lock);
+
+#define	MAX_NAME_LEN	20
+
+void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
+{
+	char name[MAX_NAME_LEN + 1];
+	struct dentry *d_top;
+
+	if (!debugfs_initialized())
+		return;
+
+	mutex_lock(&amd_iommu_debugfs_lock);
+	if (!amd_iommu_debugfs) {
+		d_top = iommu_debugfs_setup();
+		if (d_top)
+			amd_iommu_debugfs = debugfs_create_dir("amd", d_top);
+	}
+	mutex_unlock(&amd_iommu_debugfs_lock);
+	if (amd_iommu_debugfs) {
+		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu->index);
+		iommu->debugfs = debugfs_create_dir(name,
+						    amd_iommu_debugfs);
+		if (!iommu->debugfs) {
+			debugfs_remove_recursive(amd_iommu_debugfs);
+			amd_iommu_debugfs = NULL;
+		}
+	}
+}
diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 904c575d1677..031e6dbb8345 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -2721,6 +2721,7 @@ int __init amd_iommu_enable_faulting(void)
  */
 static int __init amd_iommu_init(void)
 {
+	struct amd_iommu *iommu;
 	int ret;
 
 	ret = iommu_go_to_state(IOMMU_INITIALIZED);
@@ -2730,14 +2731,15 @@ static int __init amd_iommu_init(void)
 			disable_iommus();
 			free_iommu_resources();
 		} else {
-			struct amd_iommu *iommu;
-
 			uninit_device_table_dma();
 			for_each_iommu(iommu)
 				iommu_flush_all_caches(iommu);
 		}
 	}
 
+	for_each_iommu(iommu)
+		amd_iommu_debugfs_setup(iommu);
+
 	return ret;
 }
 
diff --git a/drivers/iommu/amd_iommu_proto.h b/drivers/iommu/amd_iommu_proto.h
index 640c286a0ab9..daf7f38531f9 100644
--- a/drivers/iommu/amd_iommu_proto.h
+++ b/drivers/iommu/amd_iommu_proto.h
@@ -33,6 +33,12 @@ extern void amd_iommu_uninit_devices(void);
 extern void amd_iommu_init_notifier(void);
 extern int amd_iommu_init_api(void);
 
+#ifdef CONFIG_IOMMU_DEBUG
+void amd_iommu_debugfs_setup(struct amd_iommu *iommu);
+#else
+static inline void amd_iommu_debugfs_setup(struct amd_iommu *iommu) {}
+#endif
+
 /* Needed for interrupt remapping */
 extern int amd_iommu_prepare(void);
 extern int amd_iommu_enable(void);
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index 1c9b080276c9..2ca0959ae9e6 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -593,6 +593,9 @@ struct amd_iommu {
 
 	u32 flags;
 	volatile u64 __aligned(8) cmd_sem;
+
+	/* DebugFS Info */
+	struct dentry *debugfs;
 };
 
 static inline struct amd_iommu *dev_to_amd_iommu(struct device *dev)

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Mehta, Sohil]

On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> 
> +
> +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> +{
> +	char name[MAX_NAME_LEN + 1];
> +	struct dentry *d_top;
> +
> +	if (!debugfs_initialized())

Probably not needed.

> +		return;
> +
> +	mutex_lock(&amd_iommu_debugfs_lock);
> +	if (!amd_iommu_debugfs) {
> +		d_top = iommu_debugfs_setup();
> +		if (d_top)
> +			amd_iommu_debugfs =
> debugfs_create_dir("amd", d_top);
> +	}
> +	mutex_unlock(&amd_iommu_debugfs_lock);


You can do the above only once if you iterate over the IOMMUs here
 instead of doing it in amd_iommu_init.

> +	if (amd_iommu_debugfs) {
> +		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu-
> >index);
> +		iommu->debugfs = debugfs_create_dir(name,
> +						    amd_iommu_debugf
> s);
> +		if (!iommu->debugfs) {
> +			debugfs_remove_recursive(amd_iommu_debugfs);
> +			amd_iommu_debugfs = NULL;
> +		}
> +	}
> +}

-Sohil
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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Hook, Gary]

On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>   
>> +
>> +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
>> +{
>> +	char name[MAX_NAME_LEN + 1];
>> +	struct dentry *d_top;
>> +
>> +	if (!debugfs_initialized())
> 
> Probably not needed.

Right.

> 
>> +		return;
>> +
>> +	mutex_lock(&amd_iommu_debugfs_lock);
>> +	if (!amd_iommu_debugfs) {
>> +		d_top = iommu_debugfs_setup();
>> +		if (d_top)
>> +			amd_iommu_debugfs =
>> debugfs_create_dir("amd", d_top);
>> +	}
>> +	mutex_unlock(&amd_iommu_debugfs_lock);
> 
> 
> You can do the above only once if you iterate over the IOMMUs here
>   instead of doing it in amd_iommu_init.

I'm not sure it matters, given the finite number of IOMMUs in a system, 
and the fact that this work is done exactly once. However, removal of a 
lock is fine thing, so I'll move this around.

> 
>> +	if (amd_iommu_debugfs) {
>> +		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu-
>>> index);
>> +		iommu->debugfs = debugfs_create_dir(name,
>> +						    amd_iommu_debugf
>> s);
>> +		if (!iommu->debugfs) {
>> +			debugfs_remove_recursive(amd_iommu_debugfs);
>> +			amd_iommu_debugfs = NULL;
>> +		}
>> +	}
>> +}
> 
> -Sohil
> 

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Yang, Shunyong]

Hi, Gary and Sohil,

On Tue, 2018-04-17 at 13:38 -0400, Hook, Gary wrote:
> On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
> > 
> > On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> > > 
> > >   
> > > +
> > > +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> > > +{
> > > +	char name[MAX_NAME_LEN + 1];
> > > +	struct dentry *d_top;
> > > +
> > > +	if (!debugfs_initialized())
> > Probably not needed.
> Right.

When will this check is needed?
IMO, this function is to check debugfs ready status before we want to
use debugfs. I just want to understand when we should use
debugfs_initialized();

Thanks.
Shunyong.

> 
> > 
> > 
> > > 
> > > +		return;
> > > +
> > > +	mutex_lock(&amd_iommu_debugfs_lock);
> > > +	if (!amd_iommu_debugfs) {
> > > +		d_top = iommu_debugfs_setup();
> > > +		if (d_top)
> > > +			amd_iommu_debugfs =
> > > debugfs_create_dir("amd", d_top);
> > > +	}
> > > +	mutex_unlock(&amd_iommu_debugfs_lock);
> > 
> > You can do the above only once if you iterate over the IOMMUs here
> >   instead of doing it in amd_iommu_init.
> I'm not sure it matters, given the finite number of IOMMUs in a
> system, 
> and the fact that this work is done exactly once. However, removal of
> a 
> lock is fine thing, so I'll move this around.
> 
> > 
> > 
> > > 
> > > +	if (amd_iommu_debugfs) {
> > > +		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu-
> > > > 
> > > > index);
> > > +		iommu->debugfs = debugfs_create_dir(name,
> > > +						    amd_iommu_de
> > > bugf
> > > s);
> > > +		if (!iommu->debugfs) {
> > > +			debugfs_remove_recursive(amd_iommu_debug
> > > fs);
> > > +			amd_iommu_debugfs = NULL;
> > > +		}
> > > +	}
> > > +}
> > -Sohil
> > 
> _______________________________________________
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> https://lists.linuxfoundation.org/mailman/listinfo/iommu

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Mehta, Sohil]

On Wed, 2018-04-18 at 05:58 +0000, Yang, Shunyong wrote:
> Hi, Gary and Sohil,
> 
> On Tue, 2018-04-17 at 13:38 -0400, Hook, Gary wrote:
> > On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
> > > 
> > > On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> > > > 
> > > >   
> > > > +
> > > > +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> > > > +{
> > > > + char name[MAX_NAME_LEN + 1];
> > > > + struct dentry *d_top;
> > > > +
> > > > + if (!debugfs_initialized())
> > > Probably not needed.
> > Right.
> 
> When will this check is needed?
> IMO, this function is to check debugfs ready status before we want to
> use debugfs. I just want to understand when we should use
> debugfs_initialized();
> 

You are right debugfs_initialized() can be used to check if debugfs is
ready. However in this case we can also rely on debugfs_create_dir()
which is called in iommu_debufs_setup().

debugfs_create_dir() says:

 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 * returned.

Sohil

> Thanks.
> Shunyong.
> 
> > 
> > > 
> > > 
> > > > 
> > > > +         return;
> > > > +
> > > > + mutex_lock(&amd_iommu_debugfs_lock);
> > > > + if (!amd_iommu_debugfs) {
> > > > +         d_top = iommu_debugfs_setup();
> > > > +         if (d_top)
> > > > +                 amd_iommu_debugfs =
> > > > debugfs_create_dir("amd", d_top);
> > > > + }
> > > > + mutex_unlock(&amd_iommu_debugfs_lock);
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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Yang, Shunyong]

Hi, Sohil

On Wed, 2018-04-18 at 07:27 +0000, Mehta, Sohil wrote:
> On Wed, 2018-04-18 at 05:58 +0000, Yang, Shunyong wrote:
> > 
> > Hi, Gary and Sohil,
> > 
> > On Tue, 2018-04-17 at 13:38 -0400, Hook, Gary wrote:
> > > 
> > > On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
> > > > 
> > > >  
> > > > On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> > > > > 
> > > > >  
> > > > >   
> > > > > +
> > > > > +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> > > > > +{
> > > > > + char name[MAX_NAME_LEN + 1];
> > > > > + struct dentry *d_top;
> > > > > +
> > > > > + if (!debugfs_initialized())
> > > > Probably not needed.
> > > Right.
> > When will this check is needed?
> > IMO, this function is to check debugfs ready status before we want
> > to
> > use debugfs. I just want to understand when we should use
> > debugfs_initialized();
> > 
> You are right debugfs_initialized() can be used to check if debugfs
> is
> ready. However in this case we can also rely on debugfs_create_dir()
> which is called in iommu_debufs_setup().
> 
> debugfs_create_dir() says:
> 
>  * If debugfs is not enabled in the kernel, the value -%ENODEV will
> be
>  * returned.

It seems "If debugfs is not enabled in the kernel"
means CONFIG_DEBUG_FS is not configured. Following is the code of no
such config.

  static inline struct dentry *debugfs_create_dir(const char *name,
						struct dentry *parent)
  {
	return ERR_PTR(-ENODEV);
  }

Looking into the code, debugfs_initialized() return the value of
debugfs_registered. debugfs_registered is set to true after
debugfs_init() has been called.
However, debugfs_create_dir() doesn't call debugfs_initialized() or
check debugfs_registered value.
So, there is tiny different of checking status by debugfs_create_dir()
and debugfs_initialized(). Although it can achieve functionality here.

Maybe the original design is to call debugfs_initialized() before
calling debugfs_create_xxx()?

Thanks.
Shunyong.

> 
> Sohil
> 
> > 
> > Thanks.
> > Shunyong.
> > 
> > > 
> > >  
> > > > 
> > > >  
> > > >  
> > > > > 
> > > > >  
> > > > > +         return;
> > > > > +
> > > > > + mutex_lock(&amd_iommu_debugfs_lock);
> > > > > + if (!amd_iommu_debugfs) {
> > > > > +         d_top = iommu_debugfs_setup();
> > > > > +         if (d_top)
> > > > > +                 amd_iommu_debugfs =
> > > > > debugfs_create_dir("amd", d_top);
> > > > > + }
> > > > > + mutex_unlock(&amd_iommu_debugfs_lock);

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Mehta, Sohil]

On Wed, 2018-04-18 at 08:31 +0000, Yang, Shunyong wrote:
> Maybe the original design is to call debugfs_initialized() before
> calling debugfs_create_xxx()?

I am unaware of the original design. Someone else would probably have
more context. However, looking at other places in the kernel where
debugfs_create_xx() is used, the common convention seems to be to avoid
calling debugfs_initialized().

 Sohil

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Hook, Gary]

On 4/18/2018 4:16 PM, Mehta, Sohil wrote:
> On Wed, 2018-04-18 at 08:31 +0000, Yang, Shunyong wrote:
>> Maybe the original design is to call debugfs_initialized() before
>> calling debugfs_create_xxx()?
> 
> I am unaware of the original design. Someone else would probably have
> more context. However, looking at other places in the kernel where
> debugfs_create_xx() is used, the common convention seems to be to avoid
> calling debugfs_initialized().
> 
>   Sohil
> 

debugfs_initialized() was introduced in commit c0f92ba99 back in 
2.6.30-rc1. It was intended as a helper, not as a gatekeeper, which is 
why one doesn't see it used. Given that my use in this proposed patch is 
straightforward, I'm not seeing the need here. I had just seen some 
other code that used it, and copied the model.

Unless someone comes along to say, yes, use it, I'll not.

Gary
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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Yang, Shunyong]

Hi, Gary,

On Wed, 2018-04-18 at 16:51 -0400, Hook, Gary wrote:
> On 4/18/2018 4:16 PM, Mehta, Sohil wrote:
> > 
> > On Wed, 2018-04-18 at 08:31 +0000, Yang, Shunyong wrote:
> > > 
> > > Maybe the original design is to call debugfs_initialized() before
> > > calling debugfs_create_xxx()?
> > I am unaware of the original design. Someone else would probably
> > have
> > more context. However, looking at other places in the kernel where
> > debugfs_create_xx() is used, the common convention seems to be to
> > avoid
> > calling debugfs_initialized().
> > 
> >   Sohil
> > 
> debugfs_initialized() was introduced in commit c0f92ba99 back in 
> 2.6.30-rc1. It was intended as a helper, not as a gatekeeper, which
> is 
> why one doesn't see it used. Given that my use in this proposed patch
> is 
> straightforward, I'm not seeing the need here. I had just seen some 
> other code that used it, and copied the model.
> 
> Unless someone comes along to say, yes, use it, I'll not.
> 

I agree with you and Sohil on removing the unnecessary function
calling.

Thanks.
Shunyong.


> Gary

Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Gary R Hook]

On 04/17/2018 12:38 PM, Hook, Gary wrote:
> On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
>> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>> +
>>> +
>>> +    mutex_lock(&amd_iommu_debugfs_lock);
>>> +    if (!amd_iommu_debugfs) {
>>> +        d_top = iommu_debugfs_setup();
>>> +        if (d_top)
>>> +            amd_iommu_debugfs =
>>> debugfs_create_dir("amd", d_top);
>>> +    }
>>> +    mutex_unlock(&amd_iommu_debugfs_lock);
>>
>>
>> You can do the above only once if you iterate over the IOMMUs here
>>   instead of doing it in amd_iommu_init.
> 
> I'm not sure it matters, given the finite number of IOMMUs in a system, 
> and the fact that this work is done exactly once. However, removal of a 
> lock is fine thing, so I'll move this around.

After thinking about this, and looking at the code, I've decided to 
leave this alone.

v4 is on its way.


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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Mehta, Sohil]

On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> 
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 5eb1121d54b9..0ca250f626d9 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -11,6 +11,7 @@ obj-$(CONFIG_IOMMU_IOVA) += iova.o
>  obj-$(CONFIG_OF_IOMMU) += of_iommu.o
>  obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
>  obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o
> +obj-$(CONFIG_IOMMU_DEBUG) += amd_iommu_debugfs.o

Compiling amd_iommu_debugfs.c seems to depend only
on CONFIG_IOMMU_DEBUG. Can we prevent the code within
amd_iommu_debugfs.c from getting compiled when either CONFIG_AMD_IOMMU
or CONFIG_IOMMU_DEBUG is disabled?

>  obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
>  obj-$(CONFIG_ARM_SMMU) += arm-smmu.o
>  obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Hook, Gary]

On 4/16/2018 8:52 PM, Mehta, Sohil wrote:
> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>
>> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
>> index 5eb1121d54b9..0ca250f626d9 100644
>> --- a/drivers/iommu/Makefile
>> +++ b/drivers/iommu/Makefile
>> @@ -11,6 +11,7 @@ obj-$(CONFIG_IOMMU_IOVA) += iova.o
>>   obj-$(CONFIG_OF_IOMMU) += of_iommu.o
>>   obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
>>   obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o
>> +obj-$(CONFIG_IOMMU_DEBUG) += amd_iommu_debugfs.o
> 
> Compiling amd_iommu_debugfs.c seems to depend only
> on CONFIG_IOMMU_DEBUG. Can we prevent the code within
> amd_iommu_debugfs.c from getting compiled when either CONFIG_AMD_IOMMU
> or CONFIG_IOMMU_DEBUG is disabled?

That's a good point. My intention was that only one switch was required 
to incorporate any DebugFS support, but I see now that I didn't consider 
all of the cases.

It appears that a per-device switch is also necessary. Unless someone 
has a better idea.

>>   obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
>>   obj-$(CONFIG_ARM_SMMU) += arm-smmu.o
>>   obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o

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Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Robin Murphy]

On 17/04/18 18:42, Hook, Gary wrote:
> On 4/16/2018 8:52 PM, Mehta, Sohil wrote:
>> On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
>>>
>>> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
>>> index 5eb1121d54b9..0ca250f626d9 100644
>>> --- a/drivers/iommu/Makefile
>>> +++ b/drivers/iommu/Makefile
>>> @@ -11,6 +11,7 @@ obj-$(CONFIG_IOMMU_IOVA) += iova.o
>>>   obj-$(CONFIG_OF_IOMMU) += of_iommu.o
>>>   obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
>>>   obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o
>>> +obj-$(CONFIG_IOMMU_DEBUG) += amd_iommu_debugfs.o
>>
>> Compiling amd_iommu_debugfs.c seems to depend only
>> on CONFIG_IOMMU_DEBUG. Can we prevent the code within
>> amd_iommu_debugfs.c from getting compiled when either CONFIG_AMD_IOMMU
>> or CONFIG_IOMMU_DEBUG is disabled?
> 
> That's a good point. My intention was that only one switch was required 
> to incorporate any DebugFS support, but I see now that I didn't consider 
> all of the cases.
> 
> It appears that a per-device switch is also necessary. Unless someone 
> has a better idea.

Well, you could do a makefile-level dependency i.e.:

ifeq ($(CONFIG_IOMMU_DEBUG), y)
obj-$(CONFIG_AMD_IOMMU) += amd_iommu_debugfs.o
obj-$(CONFIG_BLAH_IOMMU) += blah_iommu_debugfs.o
...
endif

Or alternatively have an intermediate silent Kconfig option:

config AMD_IOMMU_DEBUG
	def_bool y
	depends on AMD_IOMMU && IOMMU_DEBUG

The makefile option is arguably ugly, but does at least scale better ;)

Robin.

>>>   obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
>>>   obj-$(CONFIG_ARM_SMMU) += arm-smmu.o
>>>   obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
> 
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