[PATCH v6 03/12] PCI: liveupdate: Track incoming preserved PCI devices

[Pasha Tatashin]

On Fri, 22 May 2026 20:24:01 +0000, David Matlack <dmatlack at google.com> wrote:
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 10c9b65aa242..e68ae5c172d4 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -330,7 +330,7 @@ config VGA_ARB_MAX_GPUS
>  
>  config PCI_LIVEUPDATE
>  	bool "PCI Live Update Support"
> -	depends on PCI && LIVEUPDATE
> +	depends on PCI && LIVEUPDATE && 64BIT

Please move this to the first patch, fewer changes between patches, and 
also KHO does not support anything but 64-bit mode.

>
> diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
> index 065d5af822f7..96c43b84532c 100644
> --- a/drivers/pci/liveupdate.c
> +++ b/drivers/pci/liveupdate.c
> @@ -128,13 +157,49 @@ static void pci_flb_unpreserve(struct liveupdate_flb_op_args *args)
> [ ... skip 31 lines ... ]
> +
> +err_xa_destroy:
> +	xa_destroy(&incoming->xa);
> +	kfree(incoming);
> +err_restore_free:
> +	kho_restore_free(ser);

This is the pattern we have been enforcing in other places in LUO. If 
the first retrieval fails, return the same error thereafter.

> @@ -270,6 +335,91 @@ void pci_liveupdate_unpreserve(struct pci_dev *dev)
>  }
>  EXPORT_SYMBOL_GPL(pci_liveupdate_unpreserve);
>  
> +static struct pci_flb_incoming *pci_liveupdate_flb_get_incoming(void)
> +{
> +	struct pci_flb_incoming *incoming = NULL;
> +	int ret;

Maybe make the error return static, and avoid another search through compatible 
FLBs if it failed before?

1. Add "saved_err;"; if it is set, return it right away.
2. Change all errors to use goto save_err;, and at the end of the 
function, assign ret to saved_err;

> [ ... skip 15 lines ... ]
> +	 * This could mean that no PCI FLB data was passed by the previous
> +	 * kernel, but it could also mean the previous kernel used a different
> +	 * compatibility string (i.e. a different ABI).
> +	 */
> +	if (ret == -ENOENT) {
> +		pr_info_once("No incoming FLB matched %s\n", pci_liveupdate_flb.compatible);

I would assume this is very normal, e.g., no devices were preserved but 
memfd+hugetlb was preserved. Maybe use pr_debug_once().

> +		return NULL;
> +	}
> +
> +	/*
> +	 * There is incoming FLB data that matches pci_liveupdate_flb.compatible
> +	 * but it cannot be retrieved.
> +	 */
> +	if (ret) {
> +		WARN_ONCE(ret, "Failed to retrieve incoming FLB data\n");

No need to print backtrace, please just print a warning:
pr_warn_once("Failed to retrieve incoming FLB data: %pe\n", ERR_PTR(ret));

> [ ... skip 34 lines ... ]
> +	 * through pci_liveupdate_finish(). This can happen if PCI core probes
> +	 * the same device multiple times, e.g. due to hotplug.
> +	 */
> +	if (!dev_ser->refcount) {
> +		pci_liveupdate_flb_put_incoming();
> +		return;

Pleaes use 'goto put_incoming'

> +	}
> +
> +	pci_info(dev, "Device was preserved by previous kernel across Live Update\n");
> +	dev->liveupdate.incoming = dev_ser;
> +
> +	/*
> +	 * Hold the ref on the incoming FLB until pci_liveupdate_finish() so
> +	 * that dev->liveupdate.incoming does not get freed while it is in use.
> +	 */

How would that work? If finish is not called FLB stays around until the 
next reboot.

-- 
Pasha Tatashin <pasha.tatashin at soleen.com>