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

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Date:   Fri, 30 Mar 2018 13:41:44 -0500
From:   Gary R Hook <gary.hook@....com>
To:     Tom Lendacky <thomas.lendacky@....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 03/29/2018 10:57 PM, Tom Lendacky wrote:
> 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.

Exactly. Given the approach I took, it takes another patch to take 
advantage of this. I can certainly elaborate on usage if we agree that 
this framework is acceptable.

> 
>> 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?

That, my friend is left-over cruft. Please ignore. Apologies, and thanks.

>>   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.

Dang it!

> 
>>   	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.

Again: dang it!

>> + *
>> + * 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.

Thanks.

> 
>> +
>> +/* Return a zero on failure; 1 on successful setup */
> 
> Return NULL on failure, pointer to IOMMU debugfs dentry on success.

Roger.

> 
>> +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.

Roger that.

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