linux-kernel - [PATCH v3] PCI: account for sysfs-disabled reset in pci_{slot,bus}

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Message-Id: <20250207205600.1846178-1-naravamudan@nvidia.com>
Date: Fri,  7 Feb 2025 14:56:00 -0600
From: Nishanth Aravamudan <naravamudan@...dia.com>
To: "Bjorn Helgaas" <helgaas@...nel.org>
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 v3] PCI: account for sysfs-disabled reset in pci_{slot,bus}_resettable()

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.

__pci_reset_bus()
	-> pci_bus_reset(..., PCI_RESET_PROBE)
		-> pci_bus_resettable()

__pci_reset_slot()
	-> pci_slot_reset(..., PCI_RESET_PROBE)
		-> pci_slot_resettable()

pci_reset_bus()
	-> pci_probe_reset_slot()
		-> pci_slot_reset(..., PCI_RESET_PROBE)
			-> pci_bus_resettable()
	if true:
		__pci_reset_slot()
	else:
		__pci_reset_bus()

I was able to reproduce this issue with a vfio device passed to a qemu
guest, where I had disabled PCI reset via sysfs. 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(). Before my change, this
ends up ignoring the sysfs file contents and vfio-pci happily ends 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 reset
status and reset execution are both bypassed if an administrator
disables it for a 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 v2:
 - update commit message to include more details

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 869d204a70a3..738d29375ad3 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5405,6 +5405,8 @@ 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;
@@ -5481,6 +5483,8 @@ 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