[RFC PATCH 5/5] vfio/pci: Use pci_reset_supported() in place of reset_works

[Alex Williamson <alex.williamson@nvidia.com>]

vfio-pci latches whether pci_reset_function() works at open device and
makes decisions based on this latched value at runtime.  With the
introduction of the reset_method pci-sysfs attribute, this flag can
be made stale at runtime by administrative action.  Further, with the
SR-IOV active VFs gating of pci_reset_function(), the flag can be made
stale via more subtle dependencies.

Drop the latched flag and rely on pci_reset_supported() to indicate
whether reset methods exist for the device.  This is no guarantee that
those reset methods work, nor has the RESET flag in struct
vfio_device_info ever been a guarantee of VFIO_DEVICE_RESET success.
It's only a guarantee that there are reset methods that are
applicable to the device at the instant it's called.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 9 ++++-----
 include/linux/vfio_pci_core.h    | 1 -
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 956a05ca12e5..8e42342d56d3 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -609,7 +609,6 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
 	if (ret == -EAGAIN)
 		goto out_disable_device;
 
-	vdev->reset_works = !ret;
 	pci_save_state(pdev);
 	vdev->pci_saved_state = pci_store_saved_state(pdev);
 	if (!vdev->pci_saved_state)
@@ -766,7 +765,7 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
 	if (pci_load_and_free_saved_state(pdev, &vdev->pci_saved_state)) {
 		pci_info(pdev, "%s: Couldn't reload saved state\n", __func__);
 
-		if (!vdev->reset_works)
+		if (!pci_reset_supported(pdev))
 			goto out;
 
 		pci_save_state(pdev);
@@ -785,7 +784,7 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
 	 * We can not use the "try" reset interface here, which will
 	 * overwrite the previously restored configuration information.
 	 */
-	if (vdev->reset_works) {
+	if (pci_reset_supported(pdev)) {
 		bridge = pci_upstream_bridge(pdev);
 		if (bridge && !pci_dev_trylock(bridge))
 			goto out_restore_state;
@@ -1098,7 +1097,7 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
 
 	info.flags = VFIO_DEVICE_FLAGS_PCI;
 
-	if (vdev->reset_works)
+	if (pci_reset_supported(vdev->pdev))
 		info.flags |= VFIO_DEVICE_FLAGS_RESET;
 
 	info.num_regions = VFIO_PCI_NUM_REGIONS + vdev->num_regions;
@@ -1330,7 +1329,7 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
 {
 	int ret;
 
-	if (!vdev->reset_works)
+	if (!pci_reset_supported(vdev->pdev))
 		return -EINVAL;
 
 	vfio_pci_zap_and_down_write_memory_lock(vdev);
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 9a1674c152aa..6fb599ec2919 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -121,7 +121,6 @@ struct vfio_pci_core_device {
 	/* Flags only modified on setup/release - bitfield ok */
 	bool			has_dyn_msix:1;
 	bool			pci_2_3:1;
-	bool			reset_works:1;
 	bool			extended_caps:1;
 	bool			has_vga:1;
 	bool			nointx:1;
-- 
2.53.0