[PATCH 07/10] PCI: liveupdate: Never assign resources of incoming devices

[David Matlack <dmatlack@google.com>]

Prevent the PCI core from sizing or assigning the resources of incoming
preserved devices by adding a check for pci_liveupdate_is_incoming() to
pdev_resource_assignable(). It is consulted for every resource when
sizing bridge windows, in pbus_size_io() and pbus_size_mem(), and when
building the list of resources to assign, in pdev_sort_resources().

The resources of incoming devices are claimed as programmed by the
previous kernel while scanning, and claimed resources are never sized
or reassigned. However, an incoming device may also have resources that
the previous kernel never assigned an address, e.g. a disabled ROM BAR,
which therefore cannot be claimed. Assigning one of those would write
to the device's BARs, and updating a 64-bit BAR temporarily disables
memory decoding (see pci_std_update_resource()), which would disrupt
memory transactions targeting the device's other BARs, such as P2PDMA,
or MMIO from VMs whose vCPUs keep running during kexec. Leave them
unassigned while the device is incoming instead.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 drivers/pci/setup-bus.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 4bec76950f46..b82440394ee2 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -311,6 +311,10 @@ static bool pdev_resource_assignable(struct pci_dev *dev, struct resource *res)
 	if (pci_resource_is_bridge_win(idx) && res->flags & IORESOURCE_DISABLED)
 		return false;
 
+	/* Devices preserved across Live Update keep their resources */
+	if (pci_liveupdate_is_incoming(dev))
+		return false;
+
 	return true;
 }
 
-- 
2.56.0.212.g129ede20d9-goog