Inherit bus numbers from the previous kernel during a Live Update when
one or more PCI devices are being preserved. This is necessary so that
preserved devices can DMA through the IOMMU during a Live Update
(changing bus numbers would break IOMMU translation).

Signed-off-by: David Matlack <dmatlack@google.com>
---
 drivers/pci/probe.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index af6356c5a156..ca6e5f79debb 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1351,6 +1351,20 @@ static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
 	return true;
 }
 
+static bool pci_assign_all_busses(void)
+{
+	/*
+	 * During a Live Update where devices are preserved by the previous
+	 * kernel, inherit all bus numbers assigned by the previous kernel. Bus
+	 * numbers must remain stable for preserved devices so that they can
+	 * perform DMA during the Live Update uninterrupted.
+	 */
+	if (pci_liveupdate_incoming_nr_devices())
+		return false;
+
+	return pcibios_assign_all_busses();
+}
+
 /*
  * pci_scan_bridge_extend() - Scan buses behind a bridge
  * @bus: Parent bus the bridge is on
@@ -1378,6 +1392,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 				  int max, unsigned int available_buses,
 				  int pass)
 {
+	bool assign_all_busses = pci_assign_all_busses();
 	struct pci_bus *child;
 	int is_cardbus = (dev->hdr_type == PCI_HEADER_TYPE_CARDBUS);
 	u32 buses, i, j = 0;
@@ -1424,7 +1439,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 	pci_write_config_word(dev, PCI_BRIDGE_CONTROL,
 			      bctl & ~PCI_BRIDGE_CTL_MASTER_ABORT);
 
-	if ((secondary || subordinate) && !pcibios_assign_all_busses() &&
+	if ((secondary || subordinate) && !assign_all_busses &&
 	    !is_cardbus && !broken) {
 		unsigned int cmax, buses;
 
@@ -1467,7 +1482,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 		 * do in the second pass.
 		 */
 		if (!pass) {
-			if (pcibios_assign_all_busses() || broken || is_cardbus)
+			if (assign_all_busses || broken || is_cardbus)
 
 				/*
 				 * Temporarily disable forwarding of the
@@ -1542,7 +1557,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 							max+i+1))
 					break;
 				while (parent->parent) {
-					if ((!pcibios_assign_all_busses()) &&
+					if (!assign_all_busses &&
 					    (parent->busn_res.end > max) &&
 					    (parent->busn_res.end <= max+i)) {
 						j = 1;
-- 
2.53.0.rc1.225.gd81095ad13-goog