Re: [PATCH v6 1/2] iommu - Enable debugfs exposure of IOMMU driver internals

From: Gary R Hook
Date: Fri May 11 2018 - 15:42:49 EST

On 05/11/2018 10:22 AM, Robin Murphy wrote:
Hi Gary,

Just a few trivial nitpicks below, otherwise:

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

On 11/05/18 15:34, 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 function is called from iommu_init, and creates the initial DebugFS
directory. Drivers may then call iommu_debugfs_new_driver_dir() to
instantiate a device-specific directory to expose internal data.
It will return a pointer to the new dentry structure created in
/sys/kernel/debug/iommu, or NULL in the event of a failure.

Since the IOMMU driver can not be removed from the running system, there
is no need for an "off" function.

Signed-off-by: Gary R Hook <gary.hook@xxxxxxx>
---
 drivers/iommu/Kconfig | 11 ++++++
 drivers/iommu/Makefile | 1 +
 drivers/iommu/iommu-debugfs.c | 70 +++++++++++++++++++++++++++++++++++++++++
 drivers/iommu/iommu.c | 2 +
 include/linux/iommu.h | 10 ++++++
 5 files changed, 94 insertions(+)
 create mode 100644 drivers/iommu/iommu-debugfs.c

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index f3a21343e636..ff511fa8ca7d 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
 endmenu
+config IOMMU_DEBUGFS
+ÂÂÂ bool "Export IOMMU internals in DebugFS"
+ÂÂÂ depends on DEBUG_FS
+ÂÂÂ default n

bool implicitly defaults to n anyway, so you don't really need to say it.

Roger.


+ÂÂÂ help
+ÂÂÂÂÂ Allows exposure of IOMMU device internals. This option enables
+ÂÂÂÂÂ the use of debugfs by IOMMU drivers as required. Devices can,
+ÂÂÂÂÂ at initialization time, cause the IOMMU code to create a top-level
+ÂÂÂÂÂ debug/iommu directory, and then populate a subdirectory with
+ÂÂÂÂÂ entries as required.
+
 config IOMMU_IOVA
ÂÂÂÂÂ tristate
diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index 1fb695854809..74cfbc392862 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_DEBUGFS) += 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..9df3b44aef55
--- /dev/null
+++ b/drivers/iommu/iommu-debugfs.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IOMMU driver

"driver"? ;) I'd have thought something like "IOMMU debugfs core infrastructure", but arguably it's self-evident enough that it doesn't necessarily need describing at all.

Changed to your suggestion


+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ *
+ * Author: Gary R Hook <gary.hook@xxxxxxx>
+ */
+
+#include <linux/pci.h>
+#include <linux/iommu.h>
+#include <linux/debugfs.h>
+
+static struct dentry *iommu_debugfs_dir;
+
+/**
+ * iommu_debugfs_setup - create the top-level iommu directory in debugfs
+ *
+ * Provide base enablement for using debugfs to expose internal data of an
+ * IOMMU driver. When called, this function creates the
+ * /sys/kernel/debug/iommu directory.
+ *
+ * Emit a strong warning at boot time to indicate that this feature is
+ * enabled.
+ *
+ * This function is called from iommu_init; drivers may then call
+ * iommu_debugfs_new_driver_dir() to instantiate a vendor-specific
+ * directory to be used to expose internal data.
+ */
+void iommu_debugfs_setup(void)
+{
+ÂÂÂ if (!iommu_debugfs_dir) {
+ÂÂÂÂÂÂÂ iommu_debugfs_dir = debugfs_create_dir("iommu", NULL);
+ÂÂÂÂÂÂÂ if (iommu_debugfs_dir) {
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("\n");
+ pr_warn("*************************************************************\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("**ÂÂÂÂ NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICEÂÂÂ **\n");
+ pr_warn("** **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("**Â IOMMU DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNELÂ **\n");
+ pr_warn("** **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("** This means that this kernel is built to expose internal **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("** IOMMU data structures, which may compromise security on **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("** your system.ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ **\n");
+ pr_warn("** **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("** If you see this message and you are not debugging theÂÂ **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("** kernel, report this immediately to your vendor!ÂÂÂÂÂÂÂÂ **\n");
+ pr_warn("** **\n");
+ÂÂÂÂÂÂÂÂÂÂÂ pr_warn("**ÂÂÂÂ NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICEÂÂÂ **\n");
+ pr_warn("*************************************************************\n");
+ÂÂÂÂÂÂÂ }
+ÂÂÂ }
+}
+
+/**
+ * iommu_debugfs_new_driver_dir - create a vendor directory under debugfs/iommu
+ * @vendor: name of the vendor-specific subdirectory to create
+ *
+ * This function is called by an IOMMU driver to create the top-level debugfs
+ * directory for that driver. The return value is the dentry for the requested
+ * vendor directory, or NULL in case of failure.

According to kernel-doc.rst, return values should be in a dedicated section (i.e. "Return: The dentry...") rather than as part of the function description.

A style change that happened along the way; my model was apparently older code. I've adjusted for this new style.


+ */
+struct dentry *iommu_debugfs_new_driver_dir(char *vendor)

const char *?

Sure thing.


+{
+ÂÂÂ struct dentry *d_new;
+
+ÂÂÂ d_new = debugfs_create_dir(vendor, iommu_debugfs_dir);
+
+ÂÂÂ return d_new;
+}
+EXPORT_SYMBOL_GPL(iommu_debugfs_new_driver_dir);
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d2aa23202bb9..350819f1c5e1 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1747,6 +1747,8 @@ static int __init iommu_init(void)
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ NULL, kernel_kobj);
ÂÂÂÂÂ BUG_ON(!iommu_group_kset);
+ÂÂÂ iommu_debugfs_setup();
+
ÂÂÂÂÂ return 0;
 }
 core_initcall(iommu_init);
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 19938ee6eb31..25018ac0fdab 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -698,4 +698,14 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
 #endif /* CONFIG_IOMMU_API */
+#ifdef CONFIG_IOMMU_DEBUGFS
+void iommu_debugfs_setup(void);
+struct dentry *iommu_debugfs_new_driver_dir(char *vendor);
+#else
+static inline void iommu_debugfs_setup(void) {}
+static inline struct dentry *iommu_debugfs_new_driver_dir(char *vendor) { \

Since this is a function, not a macro, it doesn't really need the line continuations.

Yep. Done. And moved the curly brace to the next line.


Robin.

+ÂÂÂ return NULL; \
+}
+#endif
+
 #endif /* __LINUX_IOMMU_H */

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