linux-kernel - [PATCH v2] PCI: account for sysfs-disabled reset in pci_{slot,bus}

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Message-Id: <20250122192241.32172-1-naravamudan@nvidia.com>
Date: Wed, 22 Jan 2025 13:22:41 -0600
From: Nishanth Aravamudan <naravamudan@...dia.com>
To:
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Raphael Norwitz <raphael.norwitz@...anix.com>,
	Amey Narkhede <ameynarkhede03@...il.com>,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jason Gunthorpe <jgg@...dia.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	kvm@...r.kernel.org
Subject: [PATCH v2] PCI: account for sysfs-disabled reset in pci_{slot,bus}_resettable()

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@...dia.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Alex Williamson <alex.williamson@...hat.com>
Cc: Raphael Norwitz <raphael.norwitz@...anix.com>
Cc: Amey Narkhede <ameynarkhede03@...il.com>
Cc: linux-pci@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: Jason Gunthorpe <jgg@...dia.com>
Cc: Yishai Hadas <yishaih@...dia.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
Cc: Kevin Tian <kevin.tian@...el.com>
Cc: kvm@...r.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