linux-kernel - [RFC PATCH 06/21] vfio/pci: Accept live update preservation request for VFIO cdev

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Message-ID: <20251018000713.677779-7-vipinsh@google.com>
Date: Fri, 17 Oct 2025 17:06:58 -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 06/21] vfio/pci: Accept live update preservation request
 for VFIO cdev

Return true in can_preserve() callback of live update file handler, if
VFIO can preserve the passed VFIO cdev file. Return -EOPNOTSUPP from
prepare() callback for now to fail any attempt to preserve VFIO cdev in
live update.

The VFIO cdev opened check ensures that the file is actually used for
VFIO cdev and not for VFIO device FD which can be obtained from the VFIO
group.

Returning true from can_preserve() tells Live Update Orchestrator that
VFIO can try to preserve the given file during live update. Actual
preservation logic will be added in future patches, therefore, for now,
prepare call will fail.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 drivers/vfio/pci/vfio_pci_liveupdate.c | 16 +++++++++++++++-
 drivers/vfio/vfio_main.c               |  3 ++-
 include/linux/vfio.h                   |  2 ++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
index 088f7698a72c..2ce2c11cb51c 100644
--- a/drivers/vfio/pci/vfio_pci_liveupdate.c
+++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
@@ -8,10 +8,17 @@
  */
 
 #include <linux/liveupdate.h>
+#include <linux/vfio.h>
 #include <linux/errno.h>
 
 #include "vfio_pci_priv.h"
 
+static int vfio_pci_liveupdate_prepare(struct liveupdate_file_handler *handler,
+				       struct file *file, u64 *data)
+{
+	return -EOPNOTSUPP;
+}
+
 static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_handler *handler,
 					u64 data, struct file **file)
 {
@@ -21,10 +28,17 @@ static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_handler *handler,
 static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *handler,
 					     struct file *file)
 {
-	return -EOPNOTSUPP;
+	struct vfio_device *device = vfio_device_from_file(file);
+
+	if (!device)
+		return false;
+
+	guard(mutex)(&device->dev_set->lock);
+	return vfio_device_cdev_opened(device);
 }
 
 static const struct liveupdate_file_ops vfio_pci_luo_fops = {
+	.prepare = vfio_pci_liveupdate_prepare,
 	.retrieve = vfio_pci_liveupdate_retrieve,
 	.can_preserve = vfio_pci_liveupdate_can_preserve,
 	.owner = THIS_MODULE,
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 38c8e9350a60..4cb47c1564f4 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -1386,7 +1386,7 @@ const struct file_operations vfio_device_fops = {
 #endif
 };
 
-static struct vfio_device *vfio_device_from_file(struct file *file)
+struct vfio_device *vfio_device_from_file(struct file *file)
 {
 	struct vfio_device_file *df = file->private_data;
 
@@ -1394,6 +1394,7 @@ static struct vfio_device *vfio_device_from_file(struct file *file)
 		return NULL;
 	return df->device;
 }
+EXPORT_SYMBOL_GPL(vfio_device_from_file);
 
 /**
  * vfio_file_is_valid - True if the file is valid vfio file
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index eb563f538dee..2443d24aa237 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -385,4 +385,6 @@ int vfio_virqfd_enable(void *opaque, int (*handler)(void *, void *),
 void vfio_virqfd_disable(struct virqfd **pvirqfd);
 void vfio_virqfd_flush_thread(struct virqfd **pvirqfd);
 
+struct vfio_device *vfio_device_from_file(struct file *file);
+
 #endif /* VFIO_H */
-- 
2.51.0.858.gf9c4a03a3a-goog