Re: [PATCH v7 1/2] iommu - Enable debugfs exposure of IOMMU driver internals
From: Gary R Hook
Date: Tue Jun 05 2018 - 12:48:58 EST
On 05/24/2018 04:18 AM, Greg KH wrote:
On Mon, May 14, 2018 at 12:20:20PM -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 f3a21343e636..2eab6a849a0a 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 need a big "DO NOT ENABLE THIS OPTION UNLESS YOU REALLY REALLY KNOW
WHAT YOU ARE DOING!!!" line here. To match up with your crazy kernel
log warning.
Otherwise distros will turn this on, I guarantee it.
Apologies for not seeing this. Notes from Greg have been going to junk
mail >:-(
I will add this text to the Kconfig item.
+
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) {
No need to care about the return value, just keep going. Nothing you
should, or should not, do depending on the return value of a debugfs
call.
Sorry. Some habits are hard to break. It just seemed that if there's no
iommu debugfs directory, nothing else needed to be done. But plowing
ahead works for me. Thank you.
+ 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;
This function can be reduced to 1 line. But really, why do you need it
at all?
My intention was to not expose the base dentry. Which means that drivers
need to call in to this file to create a vendor-specific subdirectory.
At least, that was my take-away from the discussion. But you dislike
this approach to the code, so I'm open to suggestions. At the very
least, it's now a one liner.