linux-kernel - [RFC PATCH 14/21] vfio/pci: Skip device reset on live update restored device.

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Message-ID: <20251018000713.677779-15-vipinsh@google.com>
Date: Fri, 17 Oct 2025 17:07:06 -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 14/21] vfio/pci: Skip device reset on live update restored device.

Do not reset the device when a live update preserved VFIO PCI device is
opened for the first time after kexec.

Save 'reset_works' to the device serialized state. If not saved then
this value can only be restored by performing an actual reset, which is
not desired during live update. If a device can be reset before live
update then most likely it can be reset after live update unless some
reset methods have been removed. In that case when actual reset is tried
it will return an error.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 drivers/vfio/pci/vfio_pci_core.c       | 15 ++++++++++-----
 drivers/vfio/pci/vfio_pci_liveupdate.c |  9 +++++++++
 drivers/vfio/pci/vfio_pci_priv.h       |  2 ++
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 29236b015242..186a669b68a4 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -486,12 +486,17 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
 	if (ret)
 		goto out_power;
 
-	/* If reset fails because of the device lock, fail this path entirely */
-	ret = pci_try_reset_function(pdev);
-	if (ret == -EAGAIN)
-		goto out_disable_device;
+	if (vdev->liveupdate_restore) {
+		vfio_pci_liveupdate_restore_device(vdev);
+	} else {
+		/* If reset fails because of the device lock, fail this path entirely */
+		ret = pci_try_reset_function(pdev);
+		if (ret == -EAGAIN)
+			goto out_disable_device;
+
+		vdev->reset_works = !ret;
+	}
 
-	vdev->reset_works = !ret;
 	pci_save_state(pdev);
 	vdev->pci_saved_state = pci_store_saved_state(pdev);
 	if (!vdev->pci_saved_state)
diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
index 824dba2750fe..82ff9f178fdc 100644
--- a/drivers/vfio/pci/vfio_pci_liveupdate.c
+++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
@@ -22,6 +22,7 @@ struct vfio_pci_core_device_ser {
 	u8 pci_config_map[PCI_CFG_SPACE_EXP_SIZE];
 	u8 vconfig[PCI_CFG_SPACE_EXP_SIZE];
 	u32 rbar[7];
+	u8 reset_works;
 } __packed;
 
 static int vfio_pci_liveupdate_deserialize_config(struct vfio_pci_core_device *vdev,
@@ -55,6 +56,7 @@ static int vfio_pci_lu_serialize(struct vfio_pci_core_device *vdev,
 {
 	ser->bdf = pci_dev_id(vdev->pdev);
 	vfio_pci_liveupdate_serialize_config(vdev, ser);
+	ser->reset_works = vdev->reset_works;
 	return 0;
 }
 
@@ -259,3 +261,10 @@ int vfio_pci_liveupdate_restore_config(struct vfio_pci_core_device *vdev)
 
 	return vfio_pci_liveupdate_deserialize_config(vdev, ser);
 }
+
+void vfio_pci_liveupdate_restore_device(struct vfio_pci_core_device *vdev)
+{
+	struct vfio_pci_core_device_ser *ser = vdev->liveupdate_restore;
+
+	vdev->reset_works = ser->reset_works;
+}
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 0d5aca6c2471..ee1c7c229020 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -110,12 +110,14 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
 #ifdef CONFIG_LIVEUPDATE
 void vfio_pci_liveupdate_init(void);
 int vfio_pci_liveupdate_restore_config(struct vfio_pci_core_device *vdev);
+void vfio_pci_liveupdate_restore_device(struct vfio_pci_core_device *vdev);
 #else
 static inline void vfio_pci_liveupdate_init(void) { }
 int vfio_pci_liveupdate_restore_config(struct vfio_pci_core_device *vdev)
 {
 	return -EINVAL;
 }
+void vfio_pci_liveupdate_restore_device(struct vfio_pci_core_device *vdev) { }
 #endif /* CONFIG_LIVEUPDATE */
 
 #endif
-- 
2.51.0.858.gf9c4a03a3a-goog