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Date:   Tue, 18 Jul 2023 19:45:05 +0200
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Subject: Re: [PATCH v11 1/4] vfio/migration: Add debugfs to live migration
 driver
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To:     liulongfang <liulongfang@huawei.com>, alex.williamson@redhat.com,
        jgg@nvidia.com, shameerali.kolothum.thodi@huawei.com,
        jonathan.cameron@huawei.com
Cc:     cohuck@redhat.com, linux-kernel@vger.kernel.org,
        linuxarm@openeuler.org
References: <20230630092457.54902-1-liulongfang@huawei.com>
 <20230630092457.54902-2-liulongfang@huawei.com>
From:   =?UTF-8?Q?C=c3=a9dric_Le_Goater?= <clg@redhat.com>
In-Reply-To: <20230630092457.54902-2-liulongfang@huawei.com>
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On 6/30/23 11:24, liulongfang wrote:
> From: Longfang Liu <liulongfang@huawei.com>
> 
> There are multiple devices, software and operational steps involved
> in the process of live migration. An error occurred on any node may
> cause the live migration operation to fail.
> This complex process makes it very difficult to locate and analyze
> the cause when the function fails.
> 
> In order to quickly locate the cause of the problem when the
> live migration fails, I added a set of debugfs to the vfio
> live migration driver.
> 
>      +-------------------------------------------+
>      |                                           |
>      |                                           |
>      |                  QEMU                     |
>      |                                           |
>      |                                           |
>      +---+----------------------------+----------+
>          |      ^                     |      ^
>          |      |                     |      |
>          |      |                     |      |
>          v      |                     v      |
>       +---------+--+               +---------+--+
>       |src vfio_dev|               |dst vfio_dev|
>       +--+---------+               +--+---------+
>          |      ^                     |      ^
>          |      |                     |      |
>          v      |                     |      |
>     +-----------+----+           +-----------+----+
>     |src dev debugfs |           |dst dev debugfs |
>     +----------------+           +----------------+
> 
> The entire debugfs directory will be based on the definition of
> the CONFIG_DEBUG_FS macro. If this macro is not enabled, the
> interfaces in vfio.h will be empty definitions, and the creation
> and initialization of the debugfs directory will not be executed.
> 
>     vfio
>      |
>      +---<dev_name1>
>      |    +---migration
>      |        +--state
>      |        +--hisi_acc
>      |            +--attr
>      |            +--data
>      |            +--save
>      |            +--io_test
>      |
>      +---<dev_name2>
>           +---migration
>               +--state
>               +--hisi_acc
>                   +--attr
>                   +--data
>                   +--save
>                   +--io_test
> 
> debugfs will create a public root directory "vfio" file.
> then create a dev_name() file for each live migration device.
> First, create a unified state acquisition file of "migration"
> in this device directory.
> Then, create a public live migration state lookup file "state"
> Finally, create a directory file based on the device type,
> and then create the device's own debugging files under
> this directory file.
> 
> Here, HiSilicon accelerator creates three debug files:
> attr: used to export the attribute parameters of the
> current live migration device.
> data: used to export the live migration data of the current
> live migration device.
> save: used to read the current live migration device's data
> and save it to the driver.
> io_test: used to test the IO read and write for the driver.
> 
> The live migration function of the current device can be tested by
> operating the debug files, and the functional status of the equipment
> and software at each stage can be tested step by step without
> performing the complete live migration function. And after the live
> migration is performed, the migration device data of the live migration
> can be obtained through the debug files.
> 
> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
> ---
>   drivers/vfio/Makefile       |  1 +
>   drivers/vfio/vfio.h         | 14 +++++++
>   drivers/vfio/vfio_debugfs.c | 78 +++++++++++++++++++++++++++++++++++++
>   drivers/vfio/vfio_main.c    |  9 ++++-
>   include/linux/vfio.h        |  7 ++++
>   5 files changed, 108 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/vfio/vfio_debugfs.c
> 
> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
> index 66f418aef5a9..6829c58210dc 100644
> --- a/drivers/vfio/Makefile
> +++ b/drivers/vfio/Makefile
> @@ -7,6 +7,7 @@ vfio-y += vfio_main.o \
>   vfio-$(CONFIG_IOMMUFD) += iommufd.o
>   vfio-$(CONFIG_VFIO_CONTAINER) += container.o
>   vfio-$(CONFIG_VFIO_VIRQFD) += virqfd.o
> +vfio-$(CONFIG_DEBUG_FS) += vfio_debugfs.o
>   
>   obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
>   obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 7b19c621e0e6..729c52ef579a 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -264,4 +264,18 @@ static inline void vfio_device_put_kvm(struct vfio_device *device)
>   }
>   #endif
>   
> +#ifdef CONFIG_DEBUG_FS
> +void vfio_debugfs_create_root(void);
> +void vfio_debugfs_remove_root(void);
> +
> +void vfio_device_debugfs_init(struct vfio_device *vdev);
> +void vfio_device_debugfs_exit(struct vfio_device *vdev);
> +#else
> +static inline void vfio_debugfs_create_root(void) { }
> +static inline void vfio_debugfs_remove_root(void) { }
> +
> +static inline void vfio_device_debugfs_init(struct vfio_device *vdev) { }
> +static inline void vfio_device_debugfs_exit(struct vfio_device *vdev) { }
> +#endif /* CONFIG_DEBUG_FS */
> +
>   #endif
> diff --git a/drivers/vfio/vfio_debugfs.c b/drivers/vfio/vfio_debugfs.c
> new file mode 100644
> index 000000000000..7bff30f76bd9
> --- /dev/null
> +++ b/drivers/vfio/vfio_debugfs.c
> @@ -0,0 +1,78 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023, HiSilicon Ltd.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/debugfs.h>
> +#include <linux/seq_file.h>
> +#include <linux/vfio.h>
> +#include "vfio.h"
> +
> +static struct dentry *vfio_debugfs_root;

This could be external to all VFIO. See comment below.
  
> +
> +static int vfio_device_state_read(struct seq_file *seq, void *data)
> +{
> +	struct device *vf_dev = seq->private;
> +	struct vfio_device *vdev = container_of(vf_dev, struct vfio_device, device);
> +	enum vfio_device_mig_state state;
> +	int ret;
> +
> +	ret = vdev->mig_ops->migration_get_state(vdev, &state);
> +	if (ret)
> +		return -EINVAL;
> +
> +	switch (state) {
> +	case VFIO_DEVICE_STATE_RUNNING:
> +		seq_printf(seq, "%s\n", "RUNNING");
> +		break;
> +	case VFIO_DEVICE_STATE_STOP_COPY:
> +		seq_printf(seq, "%s\n", "STOP_COPY");
> +		break;
> +	case VFIO_DEVICE_STATE_STOP:
> +		seq_printf(seq, "%s\n", "STOP");
> +		break;
> +	case VFIO_DEVICE_STATE_RESUMING:
> +		seq_printf(seq, "%s\n", "RESUMING");
> +		break;
> +	case VFIO_DEVICE_STATE_RUNNING_P2P:
> +		seq_printf(seq, "%s\n", "RESUMING_P2P");
> +		break;
> +	case VFIO_DEVICE_STATE_ERROR:
> +		seq_printf(seq, "%s\n", "ERROR");
> +		break;
> +	default:
> +		seq_printf(seq, "%s\n", "Invalid");
> +	}
> +
> +	return 0;
> +}
> +
> +void vfio_device_debugfs_init(struct vfio_device *vdev)
> +{
> +	struct dentry *vfio_dev_migration = NULL;
> +	struct device *dev = &vdev->device;
> +
> +	vdev->debug_root = debugfs_create_dir(dev_name(vdev->dev), vfio_debugfs_root);
> +	vfio_dev_migration = debugfs_create_dir("migration", vdev->debug_root);
> +
> +	debugfs_create_devm_seqfile(dev, "state", vfio_dev_migration,
> +				  vfio_device_state_read);
> +}
> +
> +void vfio_device_debugfs_exit(struct vfio_device *vdev)
> +{
> +	debugfs_remove_recursive(vdev->debug_root);
> +}

I would simply use :

	if (IS_ENABLED(CONFIG_DEBUG_FS))
		debugfs_remove_recursive(vdev->debug_root);

where vfio_device_debugfs_exit() is called.

> +
> +void vfio_debugfs_create_root(void)
> +{
> +	vfio_debugfs_root = debugfs_create_dir("vfio", NULL);
> +}
> +
> +void vfio_debugfs_remove_root(void)
> +{
> +	debugfs_remove_recursive(vfio_debugfs_root);
> +	vfio_debugfs_root = NULL;
ditto.

> +}
> +
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index f0ca33b2e1df..18d050ec9a12 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -282,7 +282,8 @@ static int __vfio_register_dev(struct vfio_device *device,
>   
>   	/* Refcounting can't start until the driver calls register */
>   	refcount_set(&device->refcount, 1);
> -
> +	if (device->mig_ops)
> +		vfio_device_debugfs_init(device);

I think we should prepare ground for more debugfs files than just migration
related things. Migration is clearly a very good candidate, but there could
be more. I have a couple out of tree patches to collect statistics on VMA
usage and resets for instance which could be included.


Thanks,

C.

>   	vfio_device_group_register(device);
>   
>   	return 0;
> @@ -339,6 +340,8 @@ void vfio_unregister_group_dev(struct vfio_device *device)
>   		}
>   	}
>   
> +	if (device->mig_ops)
> +		vfio_device_debugfs_exit(device);
>   	vfio_device_group_unregister(device);
>   
>   	/* Balances device_add in register path */
> @@ -1415,7 +1418,10 @@ static int __init vfio_init(void)
>   		goto err_dev_class;
>   	}
>   
> +
> +	vfio_debugfs_create_root();
>   	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
> +
>   	return 0;
>   
>   err_dev_class:
> @@ -1433,6 +1439,7 @@ static void __exit vfio_cleanup(void)
>   	vfio_virqfd_exit();
>   	vfio_group_cleanup();
>   	xa_destroy(&vfio_device_set_xa);
> +	vfio_debugfs_remove_root();
>   }
>   
>   module_init(vfio_init);
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 2c137ea94a3e..a114b430be31 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -62,6 +62,13 @@ struct vfio_device {
>   	struct iommufd_device *iommufd_device;
>   	bool iommufd_attached;
>   #endif
> +#ifdef CONFIG_DEBUG_FS
> +	/*
> +	 * debug_root is a static property of the vfio_device
> +	 * which must be set prior to registering the vfio_device.
> +	 */
> +	struct dentry *debug_root;
> +#endif
>   };
>   
>   /**