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Message-ID: <4915e45f-2256-42b5-838c-be2e5eda69ac@redhat.com>
Date:   Thu, 19 Oct 2023 10:30:53 +0200
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User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v17 1/2] vfio/migration: Add debugfs to live migration
 driver
Content-Language: en-US
To:     liulongfang <liulongfang@huawei.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>
From:   =?UTF-8?Q?C=C3=A9dric_Le_Goater?= <clegoate@redhat.com>
In-Reply-To: <d4a2f596-13c9-f3d3-3bbd-ee773f026341@huawei.com>
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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 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.

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,
>>>    };
>>>      /**
>>
>> .
>>
>