Re: [PATCH v9 1/5] vfio/migration: Add debugfs to live migration driver

From: liulongfang
Date: Mon Mar 20 2023 - 22:40:42 EST

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On 2023/3/21 5:33, Alex Williamson wrote:
> On Mon, 20 Mar 2023 17:23:34 +0800
> Longfang Liu <liulongfang@xxxxxxxxxx> 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
>> | +--hisi_acc
>> | +--attr
>> | +--data
>> | +--debug
>> |
>> +---<dev_name2>
>> +---migration
>> +--state
>> +--hisi_acc
>> +--attr
>> +--data
>> +--debug
>>
>> 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 obtain the attribute parameters of the
>> current live migration device.
>> data: used to get the live migration data of the current
>> live migration device.
>> debug: Used to debug the current live migration device
>> through commands.
>>
>> 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@xxxxxxxxxx>
>> ---
>> drivers/vfio/Makefile | 2 +-
>> drivers/vfio/vfio.h | 14 +++++++
>> drivers/vfio/vfio_debugfs.c | 80 +++++++++++++++++++++++++++++++++++++
>> drivers/vfio/vfio_main.c | 5 +++
>> include/linux/vfio.h | 8 ++++
>> 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 70e7dcb302ef..1debcff31d30 100644
>> --- a/drivers/vfio/Makefile
>> +++ b/drivers/vfio/Makefile
>> @@ -7,7 +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
>> obj-$(CONFIG_VFIO_PCI) += pci/
>> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
>> index e9721d8424bc..8e5cafa6aa3a 100644
>> --- a/drivers/vfio/vfio.h
>> +++ b/drivers/vfio/vfio.h
>> @@ -258,4 +258,18 @@ 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..f5b6bf2a1d48
>> --- /dev/null
>> +++ b/drivers/vfio/vfio_debugfs.c
>> @@ -0,0 +1,80 @@
>> +// 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;
>> +
>> + 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);
>
> Am I understanding correctly that there seems to be a standard with
> debugfs helpers to accept and test for bad inputs such that typical
> callers don't bother to test for ERR_PTRs from cases like above?
>

It is stated in the debugfs_create_dir interface that an error will be
returned only when CONFIG_DEBUG_FS is not enabled.

>> +
>> + debugfs_create_devm_seqfile(dev, "state", vfio_dev_migration,
>> + vfio_device_state_read);
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_device_debugfs_init);
>
> I think these should be more integrated into vfio core. As it is, this
> series doesn't enable the base migration/state entry support for
> drivers other than hisi_acc, where this proposal requires explicit
> setup and teardown by the driver probe and remove callbacks.
>
> Instead the init and exit functions here should be called directly from
> __vfio_register_dev() and vfio_unregister_group_dev() respectively.
> The setup of the migration directory and state file should be
> conditional on the device providing mig_ops, while the base dev_name
> directory is setup for all devices for future use cases.
>
> This would allow that mlx5 and future drivers automatically get this
> with no driver code, and in fact all devices would get debugfs dev_name
> directories for better test coverage. hisi_acc would only need to add
> driver specific entries after registering the device and free any
> related data after unregistering the device. In this way, none of the
> entry points here would need to be exported for drivers, which is
> perhaps the direction Jason was thinking with his prior comments.
>

I understand your plan.
I will fix it in the next version.

>> +
>> +void vfio_device_debugfs_exit(struct vfio_device *vdev)
>> +{
>> + debugfs_remove_recursive(vdev->debug_root);
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_device_debugfs_exit);
>> +
>> +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_main.c b/drivers/vfio/vfio_main.c
>> index 3a597e799918..09772fd3a396 100644
>> --- a/drivers/vfio/vfio_main.c
>> +++ b/drivers/vfio/vfio_main.c
>> @@ -1408,6 +1408,9 @@ static int __init vfio_init(void)
>> }
>>
>> pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
>> +
>> + vfio_debugfs_create_root();
>> +
>
> The pr_info is intended to be the last call in the init path.
>
OK.

>> return 0;
>>
>> err_dev_class:
>> @@ -1425,6 +1428,8 @@ static void __exit vfio_cleanup(void)
>> vfio_virqfd_exit();
>> vfio_group_cleanup();
>> xa_destroy(&vfio_device_set_xa);
>> +
>> + vfio_debugfs_remove_root();
>
> The added blank line is unnecessary, there's no conceptual reason to
> split this from the remaining teardown. I suspect this should also be
> first in the teardown since it was setup last on init and I don't see
> any other dependencies.
>OK.

>> }
>>
>> module_init(vfio_init);
>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index 93134b023968..fa6b898ebb58 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -63,6 +63,14 @@ struct vfio_device {
>> struct iommufd_ctx *iommufd_ictx;
>> 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.
>> + */
>
> What imposed this ordering requirement? In fact the code flow here
> makes the debugfs entries available event before the device is
> registered with vfio core, which seems problematic. This goes away if
> it's setup as described above. Thanks,
>
OK.
I will modify this comment.

Thanks.
Longfang.
> Alex
>
>> + struct dentry *debug_root;
>> +#endif
>> };
>>
>> /**
>
> .
>

Next message: Haifeng Xu: "Re: [RFC] memcg, oom: clean up mem_cgroup_oom_synchronize"
Previous message: Dan Williams: "Re: [PATCH] nvdimm: nvdimm_bus_register: Avoid adding device to the unregistered bus"
In reply to: liulongfang: "Re: [PATCH v9 1/5] vfio/migration: Add debugfs to live migration driver"
Next in thread: Longfang Liu: "[PATCH v9 2/5] hisi_acc_vfio_pci: extract public functions for container_of"
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