linux-kernel - [RFC PATCH 07/21] vfio/pci: Store VFIO PCI device preservation data in KHO for live update

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Message-ID: <20251018000713.677779-8-vipinsh@google.com>
Date: Fri, 17 Oct 2025 17:06:59 -0700
From: Vipin Sharma <vipinsh@...gle.com>
To: bhelgaas@...gle.com, alex.williamson@...hat.com, pasha.tatashin@...een.com, 
	dmatlack@...gle.com, jgg@...pe.ca, graf@...zon.com
Cc: pratyush@...nel.org, gregkh@...uxfoundation.org, chrisl@...nel.org, 
	rppt@...nel.org, skhawaja@...gle.com, parav@...dia.com, saeedm@...dia.com, 
	kevin.tian@...el.com, jrhilke@...gle.com, david@...hat.com, 
	jgowans@...zon.com, dwmw2@...radead.org, epetron@...zon.de, 
	junaids@...gle.com, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Vipin Sharma <vipinsh@...gle.com>
Subject: [RFC PATCH 07/21] vfio/pci: Store VFIO PCI device preservation data
 in KHO for live update

Create a struct to serialize VFIO PCI data and preserve it using KHO.
Provide physical address of the folio to Live Update Orchestrator (LUO)
in prepare() callback so that LUO can give it back after kexec.
Unpreserve and free the folio in cancel() callback.

Store PCI BDF value in the serialized data. BDF value is unique for each
device on a host and remains same unless hardware or firmware is
changed.

Preserving BDF value allows VFIO to find the PCI device which LUO wants
to restore in retrieve() callback after kexec. In future patches, more
meaningful data will be serialized to actually preserve working of the
device.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 drivers/vfio/pci/vfio_pci_liveupdate.c | 54 +++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
index 2ce2c11cb51c..3eb4895ce475 100644
--- a/drivers/vfio/pci/vfio_pci_liveupdate.c
+++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
@@ -10,13 +10,64 @@
 #include <linux/liveupdate.h>
 #include <linux/vfio.h>
 #include <linux/errno.h>
+#include <linux/kexec_handover.h>
 
 #include "vfio_pci_priv.h"
 
+struct vfio_pci_core_device_ser {
+	u16 bdf;
+} __packed;
+
+static int vfio_pci_lu_serialize(struct vfio_pci_core_device *vdev,
+				 struct vfio_pci_core_device_ser *ser)
+{
+	ser->bdf = pci_dev_id(vdev->pdev);
+	return 0;
+}
+
 static int vfio_pci_liveupdate_prepare(struct liveupdate_file_handler *handler,
 				       struct file *file, u64 *data)
 {
-	return -EOPNOTSUPP;
+	struct vfio_pci_core_device_ser *ser;
+	struct vfio_pci_core_device *vdev;
+	struct vfio_device *device;
+	struct folio *folio;
+	int err;
+
+	device = vfio_device_from_file(file);
+	vdev = container_of(device, struct vfio_pci_core_device, vdev);
+
+	folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, get_order(sizeof(*ser)));
+	if (!folio)
+		return -ENOMEM;
+
+	ser = folio_address(folio);
+
+	err = vfio_pci_lu_serialize(vdev, ser);
+	if (err)
+		goto err_free_folio;
+
+	err = kho_preserve_folio(folio);
+	if (err)
+		goto err_free_folio;
+
+	*data = virt_to_phys(ser);
+
+	return 0;
+
+err_free_folio:
+	folio_put(folio);
+	return err;
+}
+
+static void vfio_pci_liveupdate_cancel(struct liveupdate_file_handler *handler,
+				       struct file *file, u64 data)
+{
+	struct vfio_pci_core_device_ser *ser = phys_to_virt(data);
+	struct folio *folio = virt_to_folio(ser);
+
+	WARN_ON_ONCE(kho_unpreserve_folio(folio));
+	folio_put(folio);
 }
 
 static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_handler *handler,
@@ -39,6 +90,7 @@ static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *han
 
 static const struct liveupdate_file_ops vfio_pci_luo_fops = {
 	.prepare = vfio_pci_liveupdate_prepare,
+	.cancel = vfio_pci_liveupdate_cancel,
 	.retrieve = vfio_pci_liveupdate_retrieve,
 	.can_preserve = vfio_pci_liveupdate_can_preserve,
 	.owner = THIS_MODULE,
-- 
2.51.0.858.gf9c4a03a3a-goog