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SubjectRe: [PATCH v8 1/2] iommu - Enable debugfs exposure of IOMMU driver internals
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@amd.com>
> ---
> 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 :(



> +
> 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@amd.com>
> + */
> +
> +#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.

> + 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?

thanks,

greg k-h

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