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Subject: Re: [PATCH v17 1/2] vfio/migration: Add debugfs to live migration
 driver
To:     =?UTF-8?Q?C=c3=a9dric_Le_Goater?= <clegoate@redhat.com>,
        <alex.williamson@redhat.com>, <jgg@nvidia.com>,
        <shameerali.kolothum.thodi@huawei.com>,
        <jonathan.cameron@huawei.com>
CC:     <bcreeley@amd.com>, <kvm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linuxarm@openeuler.org>
References: <20231013090441.36417-1-liulongfang@huawei.com>
 <20231013090441.36417-2-liulongfang@huawei.com>
 <dee481c3-f6bd-4ba9-a2d4-528dfb668159@redhat.com>
 <d4a2f596-13c9-f3d3-3bbd-ee773f026341@huawei.com>
 <4915e45f-2256-42b5-838c-be2e5eda69ac@redhat.com>
From:   liulongfang <liulongfang@huawei.com>
Message-ID: <ee582a2f-0951-29fb-e17d-ae0622c8e85e@huawei.com>
Date:   Fri, 20 Oct 2023 17:38:31 +0800
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On 2023/10/19 16:30, Cédric Le Goater wrote:
> On 10/19/23 10:03, liulongfang wrote:
>> On 2023/10/16 23:17, Cédric Le Goater wrote:
>>> Hello Longfang,
>>>
>>> On 10/13/23 11:04, Longfang Liu wrote:
>>>> 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
>>>>       |
>>>>       +---<dev_name2>
>>>>            +---migration
>>>>                +--state
>>>>
>>>> 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".
>>>>
>>>> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
>>>> ---
>>>>    drivers/vfio/Kconfig      | 10 +++++
>>>>    drivers/vfio/Makefile     |  1 +
>>>>    drivers/vfio/debugfs.c    | 90 +++++++++++++++++++++++++++++++++++++++
>>>>    drivers/vfio/vfio.h       | 14 ++++++
>>>>    drivers/vfio/vfio_main.c  | 14 +++++-
>>>>    include/linux/vfio.h      |  7 +++
>>>>    include/uapi/linux/vfio.h |  1 +
>>>>    7 files changed, 135 insertions(+), 2 deletions(-)
>>>>    create mode 100644 drivers/vfio/debugfs.c
>>>>
>>>> diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
>>>> index 6bda6dbb4878..ceae52fd7586 100644
>>>> --- a/drivers/vfio/Kconfig
>>>> +++ b/drivers/vfio/Kconfig
>>>> @@ -80,6 +80,16 @@ config VFIO_VIRQFD
>>>>        select EVENTFD
>>>>        default n
>>>>    +config VFIO_DEBUGFS
>>>> +    bool "Export VFIO internals in DebugFS"
>>>> +    depends on DEBUG_FS
>>>> +    help
>>>> +      Allows exposure of VFIO device internals. This option enables
>>>> +      the use of debugfs by VFIO drivers as required. The device can
>>>> +      cause the VFIO code create a top-level debug/vfio directory
>>>> +      during initialization, and then populate a subdirectory with
>>>> +      entries as required.
>>>> +
>>>>    source "drivers/vfio/pci/Kconfig"
>>>>    source "drivers/vfio/platform/Kconfig"
>>>>    source "drivers/vfio/mdev/Kconfig"
>>>> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
>>>> index c82ea032d352..d43a699d55b1 100644
>>>> --- a/drivers/vfio/Makefile
>>>> +++ b/drivers/vfio/Makefile
>>>> @@ -8,6 +8,7 @@ vfio-$(CONFIG_VFIO_GROUP) += group.o
>>>>    vfio-$(CONFIG_IOMMUFD) += iommufd.o
>>>>    vfio-$(CONFIG_VFIO_CONTAINER) += container.o
>>>>    vfio-$(CONFIG_VFIO_VIRQFD) += virqfd.o
>>>> +vfio-$(CONFIG_VFIO_DEBUGFS) += debugfs.o
>>>>      obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
>>>>    obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
>>>> diff --git a/drivers/vfio/debugfs.c b/drivers/vfio/debugfs.c
>>>> new file mode 100644
>>>> index 000000000000..ae53d6110f47
>>>> --- /dev/null
>>>> +++ b/drivers/vfio/debugfs.c
>>>> @@ -0,0 +1,90 @@
>>>> +// 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;
>>>> +
>>>> +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;
>>>> +
>>>> +    BUILD_BUG_ON(VFIO_DEVICE_STATE_NR !=
>>>> +        VFIO_DEVICE_STATE_PRE_COPY_P2P + 1);
>>>> +
>>>> +    ret = vdev->mig_ops->migration_get_state(vdev, &state);
>>>> +    if (ret)
>>>> +        return -EINVAL;
>>>> +
>>>> +    switch (state) {
>>>> +    case VFIO_DEVICE_STATE_ERROR:
>>>> +        seq_printf(seq, "%s\n", "ERROR");
>>>> +        break;
>>>> +    case VFIO_DEVICE_STATE_STOP:
>>>> +        seq_printf(seq, "%s\n", "STOP");
>>>> +        break;
>>>> +    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_RESUMING:
>>>> +        seq_printf(seq, "%s\n", "RESUMING");
>>>> +        break;
>>>> +    case VFIO_DEVICE_STATE_RUNNING_P2P:
>>>> +        seq_printf(seq, "%s\n", "RUNNING_P2P");
>>>> +        break;
>>>> +    case VFIO_DEVICE_STATE_PRE_COPY:
>>>> +        seq_printf(seq, "%s\n", "PRE_COPY");
>>>> +        break;
>>>> +    case VFIO_DEVICE_STATE_PRE_COPY_P2P:
>>>> +        seq_printf(seq, "%s\n", "PRE_COPY_P2P");
>>>> +        break;
>>>> +    default:
>>>> +        seq_printf(seq, "%s\n", "Invalid");
>>>
>>> seq_puts() is more appropriate than seq_printf() above.
>>>
>>
>> There is no difference between seq_puts() and seq_printf() here,
>> no need to modify it.
> 
> seq_puts is simply preferred for unformatted output.
>

I think there is nothing wrong with using "seq_printf".

>>> I would suggest to add an array or some helper, that the VFIO drivers
>>> could use to debug the migration flow with pr_* primitives. It can be
>>> done later.
>>>
>>
>> If you want to debug this migration process in the VFIO driver,
>> you can refer to vdev->mig_ops->migration_get_state() to read the status.
>>
>>>
>>>> +    }
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +void vfio_device_debugfs_init(struct vfio_device *vdev)
>>>> +{
>>>> +    struct device *dev = &vdev->device;
>>>> +
>>>> +    vdev->debug_root = debugfs_create_dir(dev_name(vdev->dev), vfio_debugfs_root);
>>>> +
>>>> +    if (vdev->mig_ops) {
>>>> +        struct dentry *vfio_dev_migration = NULL;
>>>
>>> mig_dir maybe ?
>>>
>>
>> "vfio_dev_migration " will not affect the readability of the code.
>>
>>> It would be easier to understand the nature of the variable IMHO.
>>>
>>>> +
>>>> +        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);
>>>> +}
>>>> +
>>>> +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;
>>>> +}
>>>> +
>>>> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
>>>> index 307e3f29b527..bde84ad344e5 100644
>>>> --- a/drivers/vfio/vfio.h
>>>> +++ b/drivers/vfio/vfio.h
>>>> @@ -448,4 +448,18 @@ static inline void vfio_device_put_kvm(struct vfio_device *device)
>>>>    }
>>>>    #endif
>>>>    +#ifdef CONFIG_VFIO_DEBUGFS
>>>> +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_VFIO_DEBUGFS */
>>>> +
>>>>    #endif
>>>> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
>>>> index e31e1952d7b8..9aec4c22f051 100644
>>>> --- a/drivers/vfio/vfio_main.c
>>>> +++ b/drivers/vfio/vfio_main.c
>>>> @@ -309,7 +309,6 @@ static int __vfio_register_dev(struct vfio_device *device,
>>>>          /* Refcounting can't start until the driver calls register */
>>>>        refcount_set(&device->refcount, 1);
>>>> -
>>>
>>> superfluous change.
>>>
>>
>> A blank line here is to separate it from the comment above.
>> Makes it easier to be read.
>>
>>>>        vfio_device_group_register(device);
>>>>          return 0;
>>>> @@ -320,7 +319,15 @@ static int __vfio_register_dev(struct vfio_device *device,
>>>>      int vfio_register_group_dev(struct vfio_device *device)
>>>>    {
>>>> -    return __vfio_register_dev(device, VFIO_IOMMU);
>>>> +    int ret;
>>>> +
>>>> +    ret = __vfio_register_dev(device, VFIO_IOMMU);
>>>> +    if (ret)
>>>> +        return ret;
>>>> +
>>>> +    vfio_device_debugfs_init(device);
>>>
>>> Can it be called from __vfio_register_dev() instead ? and mdev devices
>>> would get debugfs support also.
>>>
>>
>> This is for symmetry in function calls.
>> The need for symmetry was mentioned in the previous review.
> 
> yes. But this is also exluding the mdev devices which is a large VFIO family.
>

Here it is symmetrically encoded like this. Are there any problems when using it in mdev?

Thanks,
Longfang.

> Thanks,
> 
> C.
>  
>>
>>> Thanks,
>>>
>>> C.
>>>
>> Thanks,
>> Longfang.
>>
>>>> +
>>>> +    return 0;
>>>>    }
>>>>    EXPORT_SYMBOL_GPL(vfio_register_group_dev);
>>>>    @@ -378,6 +385,7 @@ void vfio_unregister_group_dev(struct vfio_device *device)
>>>>            }
>>>>        }
>>>>    +    vfio_device_debugfs_exit(device);
>>>>        /* Balances vfio_device_set_group in register path */
>>>>        vfio_device_remove_group(device);
>>>>    }
>>>> @@ -1676,6 +1684,7 @@ static int __init vfio_init(void)
>>>>        if (ret)
>>>>            goto err_alloc_dev_chrdev;
>>>>    +    vfio_debugfs_create_root();
>>>>        pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
>>>>        return 0;
>>>>    @@ -1691,6 +1700,7 @@ static int __init vfio_init(void)
>>>>      static void __exit vfio_cleanup(void)
>>>>    {
>>>> +    vfio_debugfs_remove_root();
>>>>        ida_destroy(&vfio.device_ida);
>>>>        vfio_cdev_cleanup();
>>>>        class_destroy(vfio.device_class);
>>>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>>>> index 454e9295970c..769d7af86225 100644
>>>> --- a/include/linux/vfio.h
>>>> +++ b/include/linux/vfio.h
>>>> @@ -69,6 +69,13 @@ struct vfio_device {
>>>>        u8 iommufd_attached:1;
>>>>    #endif
>>>>        u8 cdev_opened:1;
>>>> +#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
>>>>    };
>>>>      /**
>>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>>>> index 7f5fb010226d..2b68e6cdf190 100644
>>>> --- a/include/uapi/linux/vfio.h
>>>> +++ b/include/uapi/linux/vfio.h
>>>> @@ -1219,6 +1219,7 @@ enum vfio_device_mig_state {
>>>>        VFIO_DEVICE_STATE_RUNNING_P2P = 5,
>>>>        VFIO_DEVICE_STATE_PRE_COPY = 6,
>>>>        VFIO_DEVICE_STATE_PRE_COPY_P2P = 7,
>>>> +    VFIO_DEVICE_STATE_NR,
>>>>    };
>>>>      /**
>>>
>>> .
>>>
>>
> 
> .
>