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: <aS3SJxAjVT-ZH1YT@google.com>
Date: Mon, 1 Dec 2025 17:36:39 +0000
From: David Matlack <dmatlack@...gle.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
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

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);