linux-kernel - [PATCH v2 03/22] PCI: Inherit bus numbers from previous kernel during Live Update

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Message-ID: <20260129212510.967611-4-dmatlack@google.com>
Date: Thu, 29 Jan 2026 21:24:50 +0000
From: David Matlack <dmatlack@...gle.com>
To: Alex Williamson <alex@...zbot.org>
Cc: Adithya Jayachandran <ajayachandra@...dia.com>, Alexander Graf <graf@...zon.com>, 
	Alex Mastro <amastro@...com>, Alistair Popple <apopple@...dia.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Ankit Agrawal <ankita@...dia.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Chris Li <chrisl@...nel.org>, 
	David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>, 
	Jacob Pan <jacob.pan@...ux.microsoft.com>, Jason Gunthorpe <jgg@...dia.com>, 
	Jason Gunthorpe <jgg@...pe.ca>, Jonathan Corbet <corbet@....net>, Josh Hilke <jrhilke@...gle.com>, 
	Kevin Tian <kevin.tian@...el.com>, kexec@...ts.infradead.org, kvm@...r.kernel.org, 
	Leon Romanovsky <leon@...nel.org>, Leon Romanovsky <leonro@...dia.com>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, linux-pci@...r.kernel.org, Lukas Wunner <lukas@...ner.de>, 
	"Michał Winiarski" <michal.winiarski@...el.com>, Mike Rapoport <rppt@...nel.org>, 
	Parav Pandit <parav@...dia.com>, Pasha Tatashin <pasha.tatashin@...een.com>, 
	Pranjal Shrivastava <praan@...gle.com>, Pratyush Yadav <pratyush@...nel.org>, 
	Raghavendra Rao Ananta <rananta@...gle.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Saeed Mahameed <saeedm@...dia.com>, Samiullah Khawaja <skhawaja@...gle.com>, 
	Shuah Khan <skhan@...uxfoundation.org>, 
	"Thomas Hellström" <thomas.hellstrom@...ux.intel.com>, Tomita Moeko <tomitamoeko@...il.com>, 
	Vipin Sharma <vipinsh@...gle.com>, Vivek Kasireddy <vivek.kasireddy@...el.com>, 
	William Tu <witu@...dia.com>, Yi Liu <yi.l.liu@...el.com>, Zhu Yanjun <yanjun.zhu@...ux.dev>
Subject: [PATCH v2 03/22] PCI: Inherit bus numbers from previous kernel during
 Live Update

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@...gle.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