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

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Date:   Thu, 29 Mar 2018 22:57:11 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Gary R Hook <gary.hook@....com>, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, jacob.jun.pan@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iommu - Enable debugfs exposure of the IOMMU

On 3/29/2018 5:54 PM, Gary R Hook wrote:
> Provide base enablement for using debugfs to expose internal data of
> an IOMMU driver. When enabled, create the /sys/kernel/debug/iommu

So this can't actually create anything yet since nothing invokes the
function.  Maybe describe how it should be used by other drivers (and
probably include that description as a commment for the function) to
create the directory.

> directory.  Emit a strong warning at boot time to indicate that this
> feature is enabled.
> 
> Signed-off-by: Gary R Hook <gary.hook@....com>
> ---
>  drivers/iommu/Kconfig          |   11 +++++++++++
>  drivers/iommu/Makefile         |    2 ++
>  drivers/iommu/amd_iommu_init.c |    2 ++
>  drivers/iommu/iommu-debugfs.c  |   32 ++++++++++++++++++++++++++++++++
>  include/linux/iommu.h          |    4 ++++
>  5 files changed, 51 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..5e5c3339681d 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-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
> @@ -10,6 +11,7 @@ obj-$(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_AMD_IOMMU_DEBUG) += amd_iommu_debugfs.o

Where is this CONFIG defined?

>  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_init.c b/drivers/iommu/amd_iommu_init.c
> index 6fe2d0346073..99d48c42a12f 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -2783,6 +2783,8 @@ int __init amd_iommu_detect(void)
>  	iommu_detected = 1;
>  	x86_init.iommu.iommu_init = amd_iommu_init;
>  
> +dump_stack();
> +

This definitely shouldn't be here.

>  	return 1;
>  }
>  
> diff --git a/drivers/iommu/iommu-debugfs.c b/drivers/iommu/iommu-debugfs.c
> new file mode 100644
> index 000000000000..94c9acc63b65
> --- /dev/null
> +++ b/drivers/iommu/iommu-debugfs.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * AMD IOMMU driver

This isn't the AMD IOMMU driver.

> + *
> + * Copyright (C) 2018 Advanced Micro Devices, Inc.
> + *
> + * Author: Gary R Hook <gary.hook@....com>
> + */
> +
> +#include <linux/pci.h>
> +#include <linux/iommu.h>
> +#include <linux/debugfs.h>
> +
> +static struct dentry *iommu_debugfs_dir;
> +
> +#define	MAX_NAME_LEN	20

This isn't used anywhere.

> +
> +/* Return a zero on failure; 1 on successful setup */

Return NULL on failure, pointer to IOMMU debugfs dentry on success.

> +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 41b8c5757859..cb2957dac43b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -696,6 +696,10 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
>  	return NULL;
>  }
>  
> +#ifdef	CONFIG_IOMMU_DEBUG

Should be a space between the #ifdef and the CONFIG_..., not a tab.

Thanks,
Tom

> +struct dentry *iommu_debugfs_setup(void);
> +#endif
> +
>  #endif /* CONFIG_IOMMU_API */
>  
>  #endif /* __LINUX_IOMMU_H */
>