Re: [PATCH v2 04/22] vfio/pci: Register a file handler with Live Update Orchestrator

Pranjal Shrivastava
2026-02-25T22:06:29Z

On Wed, Feb 25, 2026 at 02:33:28PM -0700, Alex Williamson wrote:
> On Thu, 29 Jan 2026 21:24:51 +0000
> David Matlack <dmatlack@google.com> wrote:
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 0c771064c0b8..19e88322af2c 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -258,6 +258,10 @@ static int __init vfio_pci_init(void)
> > int ret;
> > bool is_disable_vga = true;
> >
> > + ret = vfio_pci_liveupdate_init();
> > + if (ret)
> > + return ret;
> > +
> > #ifdef CONFIG_VFIO_PCI_VGA
> > is_disable_vga = disable_vga;
> > #endif
> > @@ -266,8 +270,10 @@ static int __init vfio_pci_init(void)
> >
> > /* Register and scan for devices */
> > ret = pci_register_driver(&vfio_pci_driver);
> > - if (ret)
> > + if (ret) {
> > + vfio_pci_liveupdate_cleanup();
> > return ret;
> > + }
> >
> > vfio_pci_fill_ids();
> >
> > @@ -281,6 +287,7 @@ module_init(vfio_pci_init);
> > static void __exit vfio_pci_cleanup(void)
> > {
> > pci_unregister_driver(&vfio_pci_driver);
> > + vfio_pci_liveupdate_cleanup();
> > }
> > module_exit(vfio_pci_cleanup);
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> > new file mode 100644
> > index 000000000000..b84e63c0357b
> > --- /dev/null
> > +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> > @@ -0,0 +1,69 @@
> ...
> > +static const struct liveupdate_file_ops vfio_pci_liveupdate_file_ops = {
> > + .can_preserve = vfio_pci_liveupdate_can_preserve,
> > + .preserve = vfio_pci_liveupdate_preserve,
> > + .unpreserve = vfio_pci_liveupdate_unpreserve,
> > + .retrieve = vfio_pci_liveupdate_retrieve,
> > + .finish = vfio_pci_liveupdate_finish,
> > + .owner = THIS_MODULE,
> > +};
> > +
> > +static struct liveupdate_file_handler vfio_pci_liveupdate_fh = {
> > + .ops = &vfio_pci_liveupdate_file_ops,
> > + .compatible = VFIO_PCI_LUO_FH_COMPATIBLE,
> > +};
> > +
> > +int __init vfio_pci_liveupdate_init(void)
> > +{
> > + if (!liveupdate_enabled())
> > + return 0;
> > +
> > + return liveupdate_register_file_handler(&vfio_pci_liveupdate_fh);
> > +}
>
> liveupdate_register_file_handler() "pins" vfio-pci with a
> try_module_get(). Since this is done in our module_init function and
> unregister occurs in our module_exit function, rather than relative
> to any actual device binding or usage, this means vfio-pci CANNOT be
> unloaded. That seems bad. Thanks,

Hmm... IIUC the concern here is about liveupdate policy if the user
wants to unload a module which was previously marked for preservation?

AFAICT, In such a case, the user is expected to close the LUO session FD,
which "unpreserves" the FD. Finally, when rmmod is executed, the __exit
(vfio_pci_cleanup) calls vfio_pci_liveupdate_cleanup() which ends up
calling liveupdate_unregister_file_handler(), thereby dropping the ref
held by the liveupdate orchestrator which allows the module to be
unloaded.

I think we should document this policy somewhere or have a dev_warn to
scream at the users when they try unloading the module without closing
the session FD.

Thanks,
Praan

>
> Alex
>
> > +
> > +void vfio_pci_liveupdate_cleanup(void)
> > +{
> > + if (!liveupdate_enabled())
> > + return;
> > +
> > + liveupdate_unregister_file_handler(&vfio_pci_liveupdate_fh);
> > +}