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Date: Thu, 19 Oct 2023 10:30:53 +0200
From: Cédric Le Goater <clegoate@...hat.com>
To: liulongfang <liulongfang@...wei.com>, alex.williamson@...hat.com,
jgg@...dia.com, shameerali.kolothum.thodi@...wei.com,
jonathan.cameron@...wei.com
Cc: bcreeley@....com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linuxarm@...neuler.org
Subject: Re: [PATCH v17 1/2] vfio/migration: Add debugfs to live migration
driver
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@...wei.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,
>>> };
>>> /**
>>
>> .
>>
>
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