linux-kernel - Re: [PATCH 00/21] vfio/pci: Base support to preserve a VFIO device file across Live Update

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Message-ID: <daf0f7a1-8791-4d3a-a4f2-66143a591466@linux.dev>
Date: Mon, 1 Dec 2025 21:50:20 -0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: David Matlack <dmatlack@...gle.com>
Cc: Alex Williamson <alex@...zbot.org>,
 Adithya Jayachandran <ajayachandra@...dia.com>, Alex Mastro
 <amastro@...com>, Alistair Popple <apopple@...dia.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Chris Li <chrisl@...nel.org>,
 David Rientjes <rientjes@...gle.com>,
 Jacob Pan <jacob.pan@...ux.microsoft.com>, Jason Gunthorpe <jgg@...dia.com>,
 Jason Gunthorpe <jgg@...pe.ca>, Josh Hilke <jrhilke@...gle.com>,
 Kevin Tian <kevin.tian@...el.com>, kvm@...r.kernel.org,
 Leon Romanovsky <leonro@...dia.com>, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-pci@...r.kernel.org,
 Lukas Wunner <lukas@...ner.de>, Mike Rapoport <rppt@...nel.org>,
 Parav Pandit <parav@...dia.com>, Pasha Tatashin <pasha.tatashin@...een.com>,
 Philipp Stanner <pstanner@...hat.com>, Pratyush Yadav <pratyush@...nel.org>,
 Saeed Mahameed <saeedm@...dia.com>, Samiullah Khawaja <skhawaja@...gle.com>,
 Shuah Khan <shuah@...nel.org>, Tomita Moeko <tomitamoeko@...il.com>,
 Vipin Sharma <vipinsh@...gle.com>, William Tu <witu@...dia.com>,
 Yi Liu <yi.l.liu@...el.com>, Yunxiang Li <Yunxiang.Li@....com>
Subject: Re: [PATCH 00/21] vfio/pci: Base support to preserve a VFIO device
 file across Live Update


在 2025/12/1 9:36, David Matlack 写道:
> On 2025-12-01 05:32 PM, David Matlack wrote:
>> On 2025-12-01 09:16 AM, Zhu Yanjun wrote:
>>> 在 2025/12/1 9:10, David Matlack 写道:
>>>> On Mon, Dec 1, 2025 at 7:49 AM Zhu Yanjun <yanjun.zhu@...ux.dev> wrote:
>>>>> 在 2025/11/27 20:56, Zhu Yanjun 写道:
>>>>>> Hi, David
>>>>>>
>>>>>> ERROR: modpost: "liveupdate_register_file_handler" [drivers/vfio/pci/
>>>>>> vfio-pci-core.ko] undefined!
>>>>>>
>>>>>> ERROR: modpost: "vfio_pci_ops" [drivers/vfio/pci/vfio-pci-core.ko]
>>>>>> undefined!
>>>>>> ERROR: modpost: "liveupdate_enabled" [drivers/vfio/pci/vfio-pci-core.ko]
>>>>>> undefined!
>>>>>> ERROR: modpost: "liveupdate_unregister_file_handler" [drivers/vfio/pci/
>>>>>> vfio-pci-core.ko] undefined!
>>>>>> ERROR: modpost: "vfio_device_fops" [drivers/vfio/pci/vfio-pci-core.ko]
>>>>>> undefined!
>>>>>> ERROR: modpost: "vfio_pci_is_intel_display" [drivers/vfio/pci/vfio-pci-
>>>>>> core.ko] undefined!
>>>>>> ERROR: modpost: "vfio_pci_liveupdate_init" [drivers/vfio/pci/vfio-
>>>>>> pci.ko] undefined!
>>>>>> ERROR: modpost: "vfio_pci_liveupdate_cleanup" [drivers/vfio/pci/vfio-
>>>>>> pci.ko] undefined!
>>>>>> make[4]: *** [scripts/Makefile.modpost:147: Module.symvers] Error 1
>>>>>> make[3]: *** [Makefile:1960: modpost] Error 2
>>>>>>
>>>>>> After I git clone the source code from the link https://github.com/
>>>>>> dmatlack/linux/tree/liveupdate/vfio/cdev/v1,
>>>>>>
>>>>>> I found the above errors when I built the source code.
>>>>>>
>>>>>> Perhaps the above errors can be solved by EXPORT_SYMBOL.
>>>>>>
>>>>>> But I am not sure if a better solution can solve the above problems or not.
>>>>> I reviewed this patch series in detail. If I’m understanding it
>>>>> correctly, there appears to be a cyclic dependency issue. Specifically,
>>>>> some functions in kernel module A depend on kernel module B, while at
>>>>> the same time certain functions in module B depend on module A.
>>>>>
>>>>> I’m not entirely sure whether this constitutes a real problem or if it’s
>>>>> intentional design.
>>>> Thanks for your report. Can you share the .config file you used to
>>>> generate these errors?
>>>
>>> IIRC, I used FC 42 default config. Perhaps you can make tests with it. If
>>> this problem can not be reproduced, I will share my config with you.
>>>
>> What does "FC 42 default config" mean?
>>
>> Either way I was able to reproduce the errors you posted above by
>> changing CONFIG_VFIO_PCI{_CORE} from "y" to "m".
>>
>> To unblock building and testing this series you can change these configs
>> from "m" to "y", or the following patch (which fixed things for me):
> Oops, sorry, something went wrong when I posted that diff. Here's the
> correct diff:
>
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 929df22c079b..c2cca16e99a8 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -2,11 +2,11 @@
>
>   vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
>   vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
> -vfio-pci-core-$(CONFIG_LIVEUPDATE) += vfio_pci_liveupdate.o
>   obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
>
>   vfio-pci-y := vfio_pci.o
>   vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
> +vfio-pci-$(CONFIG_LIVEUPDATE) += vfio_pci_liveupdate.o
>   obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
>
>   obj-$(CONFIG_MLX5_VFIO_PCI)           += mlx5/
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index c5b5eb509474..b9805861763a 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -1386,6 +1386,7 @@ const struct file_operations vfio_device_fops = {
>          .show_fdinfo    = vfio_device_show_fdinfo,
>   #endif
>   };
> +EXPORT_SYMBOL_GPL(vfio_device_fops);
>
>   /**
>    * vfio_file_is_valid - True if the file is valid vfio file
> diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
> index 69298d82f404..c7a0c9c3b6a8 100644
> --- a/kernel/liveupdate/luo_core.c
> +++ b/kernel/liveupdate/luo_core.c
> @@ -256,6 +256,7 @@ bool liveupdate_enabled(void)
>   {
>          return luo_global.enabled;
>   }
> +EXPORT_SYMBOL_GPL(liveupdate_enabled);
>
>   /**
>    * DOC: LUO ioctl Interface
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> index fca3806dae28..9baa88966f04 100644
> --- a/kernel/liveupdate/luo_file.c
> +++ b/kernel/liveupdate/luo_file.c
> @@ -868,6 +868,7 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
>          luo_session_resume();
>          return err;
>   }
> +EXPORT_SYMBOL_GPL(liveupdate_register_file_handler);
>
>   /**
>    * liveupdate_unregister_file_handler - Unregister a liveupdate file handler
> @@ -913,3 +914,4 @@ int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
>          liveupdate_test_register(fh);
>          return err;
>   }
> +EXPORT_SYMBOL_GPL(liveupdate_unregister_file_handler);

Hi, David

Thanks. The above changes resolve the EXPORT_SYMBOL_GPL issue as well as 
the cyclic dependency problem.

I recommend submitting this as a new commit, as it effectively addresses 
the issues present in the patch series.

Yanjun.Zhu

-- 
Best Regards,
Yanjun.Zhu