[PATCH v2] PCI: account for sysfs-disabled reset in pci_{slot,bus}_resettable()

Nishanth Aravamudan
2025-01-22T19:22:45Z

Both vfio_pci_ioctl_get_pci_hot_reset_info() and
vfio_pci_ioctl_pci_hot_reset() check if either the vdev's slot or bus is
not resettable by calling pci_probe_reset_{slot,bus}(). Those functions
in turn call pci_{slot,bus}_resettable() to see if the PCI device
supports reset.

However, commit d88f521da3ef ("PCI: Allow userspace to query and set
device reset mechanism") added support for userspace to disable reset of
specific PCI devices (by echo'ing "" into reset_method) and
pci_{slot,bus}_resettable() methods do not check pci_reset_supported()
to see if userspace has disabled reset. Therefore, if an administrator
disables PCI reset of a specific device, but then uses vfio-pci with
that device (e.g. with qemu), vfio-pci will happily end up issuing a
reset to that device.

Add an explicit check of pci_reset_supported() in both
pci_slot_resettable() and pci_bus_resettable() to ensure both the hot
reset status and hot reset execution are both bypassed if an
administrator disables it for a vfio-pci managed device.

Fixes: d88f521da3ef ("PCI: Allow userspace to query and set device reset mechanism")
Signed-off-by: Nishanth Aravamudan <naravamudan@nvidia.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Raphael Norwitz <raphael.norwitz@nutanix.com>
Cc: Amey Narkhede <ameynarkhede03@gmail.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Yishai Hadas <yishaih@nvidia.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: kvm@vger.kernel.org

---

Changes since v1:
- fix capitalization and ()s
- clarify same checks are done in reset path
---
drivers/pci/pci.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 661f98c6c63a..809936e1c3b7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5536,6 +5536,8 @@ static bool pci_bus_resettable(struct pci_bus *bus)
return false;

list_for_each_entry(dev, &bus->devices, bus_list) {
+ if (!pci_reset_supported(dev))
+ return false;
if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
(dev->subordinate && !pci_bus_resettable(dev->subordinate)))
return false;
@@ -5612,6 +5614,8 @@ static bool pci_slot_resettable(struct pci_slot *slot)
list_for_each_entry(dev, &slot->bus->devices, bus_list) {
if (!dev->slot || dev->slot != slot)
continue;
+ if (!pci_reset_supported(dev))
+ return false;
if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
(dev->subordinate && !pci_bus_resettable(dev->subordinate)))
return false;
--
2.34.1