Re: [PATCH v8 1/2] iommu - Enable debugfs exposure of IOMMU driver internals
From: Gary R Hook
Date: Tue Jun 05 2018 - 13:01:54 EST
On 05/29/2018 01:41 PM, Greg KH wrote:
On Tue, May 29, 2018 at 01:23:14PM -0500, 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 | 10 ++++++
drivers/iommu/Makefile | 1 +
drivers/iommu/iommu-debugfs.c | 72 +++++++++++++++++++++++++++++++++++++++++
drivers/iommu/iommu.c | 2 +
include/linux/iommu.h | 11 ++++++
5 files changed, 96 insertions(+)
create mode 100644 drivers/iommu/iommu-debugfs.c
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index c76157e57f6b..f9af25ac409f 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -60,6 +60,16 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
endmenu
+config IOMMU_DEBUGFS
+ bool "Export IOMMU internals in DebugFS"
+ depends on DEBUG_FS
+ 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.
You didn't put a big enough warning here, like I asked last time :(
As I noted a few moments ago, I didn't see these until now. Very
annoying, that.
+
config IOMMU_IOVA
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..bb1bf2d0ac51
--- /dev/null
+++ b/drivers/iommu/iommu-debugfs.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IOMMU debugfs core infrastructure
+ *
+ * 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)
+{
+ if (!iommu_debugfs_dir) {
+ iommu_debugfs_dir = debugfs_create_dir("iommu", NULL);
+ if (iommu_debugfs_dir) {
Again, no, never test a return value from a debugfs call. You do not
care, you should do the same exact thing if it is enabled or disabled or
somehow failing. Just keep moving on.
Yes, noted.
+ pr_warn("\n");
+ pr_warn("*************************************************************\n");
+ pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warn("** **\n");
+ pr_warn("** IOMMU DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL **\n");
+ pr_warn("** **\n");
+ pr_warn("** This means that this kernel is built to expose internal **\n");
+ pr_warn("** IOMMU data structures, which may compromise security on **\n");
+ pr_warn("** your system. **\n");
+ pr_warn("** **\n");
+ pr_warn("** If you see this message and you are not debugging the **\n");
+ pr_warn("** kernel, report this immediately to your vendor! **\n");
+ pr_warn("** **\n");
+ pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warn("*************************************************************\n");
+ }
+ }
+}
+
+/**
+ * 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.
+ *
+ * Return: upon success, a pointer to the dentry for the new directory.
+ * NULL in case of failure.
+ */
+struct dentry *iommu_debugfs_new_driver_dir(const char *vendor)
+{
+ struct dentry *d_new;
+
+ d_new = debugfs_create_dir(vendor, iommu_debugfs_dir);
+
+ return d_new;
+}
+EXPORT_SYMBOL_GPL(iommu_debugfs_new_driver_dir);
Why are you wrapping a debugfs call? Why not just export
iommu_debugfs_dir instead?
It was a choice, as I stated in my other post. It is not a requirement.
If you resolutely reject this approach, that's fine. I'll change it, no
worries.