Re: [PATCH v6 01/12] PCI: liveupdate: Set up FLB handler for the PCI core

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Fri, 22 May 2026 20:23:59 +0000, David Matlack <dmatlack@google.com> wrote:
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2fb1c75afd16..6c618830cf61 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -20530,6 +20530,16 @@ L:	linux-pci@vger.kernel.org
>  S:	Supported
>  F:	Documentation/PCI/pci-error-recovery.rst
>  
> +PCI LIVE UPDATE
> +M:	David Matlack <dmatlack@google.com>

Please add Pratyush, Mike, and myself so we are notified directly of 
incoming patches, the same as with other areas where the liveupdate/ 
tree is specified.

>
> diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
> new file mode 100644
> index 000000000000..737e7b9366db
> --- /dev/null
> +++ b/drivers/pci/liveupdate.c
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (c) 2026, Google LLC.
> + * David Matlack <dmatlack@google.com>
> + */
> +
> +/**
> + * DOC: PCI Live Update
> + *
> + * The PCI subsystem participates in the Live Update process to enable drivers
> + * to preserve their PCI devices across kexec.
> + *
> + * File-Lifecycle-Bound (FLB) Data
> + * ===============================

...

> + *
> + * PCI device preservation across Live Update is built on top of the Live Update
> + * Orchestrator's (LUO) support for file preservation across kexec. Drivers

I prefer to just use acronyms FLB, and LUO, but have links to the actual 
documentations about them.

So, something like this:

  * :ref:`FLB <flb>` Data
  * =====================
  *
  * PCI device preservation across Live Update is built on top of the
  * :ref:`LUO <luo>` support for file preservation across kexec. Drivers

And also add _luo and _flb to Documentation/core-api/liveupdate.rst

.. _luo:

 ========================
 Live Update Orchestrator
 ========================

.. _flb:

 LUO File Lifecycle Bound Global Data
 ====================================

> [ ... skip 17 lines ... ]
> + *
> + *  * ``pci_liveupdate_register_flb(driver_file_handler)``
> + *  * ``pci_liveupdate_unregister_flb(driver_file_handler)``
> + */
> +
> +#define pr_fmt(fmt) "PCI: liveupdate: " fmt

Nit, may be:

> +
> +#include <linux/io.h>
> +#include <linux/kexec_handover.h>
> +#include <linux/kho/abi/pci.h>
> +#include <linux/liveupdate.h>
> +#include <linux/mutex.h>
> +#include <linux/mm.h>

Please sort alphabetically.

> [ ... skip 12 lines ... ]
> +	 * future to increase the chances that there is enough room to preserve
> +	 * devices that are not yet present on the system (e.g. VFs, hot-plugged
> +	 * devices).
> +	 */
> +	for_each_pci_dev(dev)
> +		max_nr_devices++;

I think, we want to use kho_block [1] (it is in liveupdate/next branch) 
to allow number of supported devices to be dynamic.

To support this, we would redefine the ABI and tracking structures like 
so:

/* include/linux/kho/abi/pci.h */
struct pci_ser {
	u64 devices;      /* Phys address of the first block header of kho_block_set */
	u64 nr_devices;   /* Total count of active preserved devices */
} __packed;

/* drivers/pci/liveupdate.c */
struct pci_flb_outgoing {
	struct pci_ser *ser;            /* Points to the FDT/KHO-allocated ABI struct */
	struct kho_block_set block_set;  /* Controls the active blocks on the fly */
};

In  __pci_liveupdate_preserve_device() , we would search for 
and reuse any inactive  pci_dev_ser  slot first, and only call 
kho_block_set_grow() to expand if no inactive slots are available.

In pci_liveupdate_unpreserve_device(), we would simply 
mark the  pci_dev_ser as inactive.

>
> diff --git a/include/linux/pci_liveupdate.h b/include/linux/pci_liveupdate.h
> new file mode 100644
> index 000000000000..8ec98beefcb4
> --- /dev/null
> +++ b/include/linux/pci_liveupdate.h
> @@ -0,0 +1,30 @@
> [ ... skip 24 lines ... ]
> +static inline void pci_liveupdate_unregister_flb(struct liveupdate_file_handler *fh)
> +{
> +}
> +#endif
> +
> +#endif /* LINUX_PCI_LIVEUPDATE_H */

[1] https://lore.kernel.org/all/20260603154402.468928-1-pasha.tatashin@soleen.com/

Preserving: In  __pci_liveupdate_preserve_device() , we would search for 
Unpreserving: In  pci_liveupdate_unpreserve_device(), we would simply

Preserving: In  __pci_liveupdate_preserve_device() , we would search for 
Unpreserving: In  pci_liveupdate_unpreserve_device(), we would simply 

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