git: d701acea1e63 - stable/15 - pci: Do not reconcile MPS across PCI domains

The branch stable/15 has been updated by kbowling:

URL: https://cgit.FreeBSD.org/src/commit/?id=d701acea1e638304aa8099dd54ea6a639c31490d

commit d701acea1e638304aa8099dd54ea6a639c31490d
Author:     Kevin Bowling <kbowling@FreeBSD.org>
AuthorDate: 2026-08-14 05:16:41 +0000
Commit:     Kevin Bowling <kbowling@FreeBSD.org>
CommitDate: 2026-08-21 00:34:12 +0000

    pci: Do not reconcile MPS across PCI domains
    
    A PCI function can provide a host bridge into a synthetic PCI domain.
    Intel VMD does this: the host facing VMD function remains in its
    original domain while the hidden Root Ports and endpoints appear in a
    separate domain.  The VMD function's Device Control does not describe
    an upstream link in that synthetic hierarchy.
    
    The hierarchy wide cold pass incorrectly used the VMD function's MPS
    to reprogram the hidden ports and their endpoints.  Stop both cold
    reconciliation and runtime path walks at a PCI domain boundary.  The
    real Root Ports within the VMD domain continue to reconcile their
    endpoints normally.
    
    Reviewed by:    imp
    Tested by:      Michael Butler <imb@protected-networks.net>
    Fixes:          8e9fe9996a1f ("pci: Reconcile MPS before attaching PCIe devices")
    Sponsored by:   BBOX.io
    Differential Revision:  https://reviews.freebsd.org/D58837
    
    (cherry picked from commit 57293f4541cdea8e4158f751a4439f69b3ec1711)
---
 sys/dev/pci/pci.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/sys/dev/pci/pci.c b/sys/dev/pci/pci.c
index f40f68a48db9..a3cfd45e72ba 100644
--- a/sys/dev/pci/pci.c
+++ b/sys/dev/pci/pci.c
@@ -4489,6 +4489,13 @@ pcie_path_mps(device_t dev, uint16_t *mpsp)
 		pcib = device_get_parent(bus);
 		if (pcib == NULL || !is_pci_device(pcib))
 			break;
+		/*
+		 * A PCI function may expose a host bridge for a synthetic PCI
+		 * domain.  Its Device Control belongs to the parent domain and
+		 * does not describe an upstream link in the synthetic hierarchy.
+		 */
+		if (pci_get_domain(pcib) != pci_get_domain(dev))
+			break;
 		dinfo = device_get_ivars(pcib);
 		if (dinfo->cfg.pcie.pcie_location != 0) {
 			mps = pcie_read_config(pcib, PCIER_DEVICE_CTL, 2) &
@@ -4706,6 +4713,13 @@ pcie_reconcile_link_mps(device_t bus)
 	pcib = device_get_parent(bus);
 	if (!is_pci_device(pcib))
 		return;
+	/*
+	 * A PCI function may provide a host bridge into a separate domain,
+	 * as Intel VMD does.  Do not treat the function's host-facing PCIe
+	 * Device Control as the upstream end of a link in the child domain.
+	 */
+	if (pci_get_domain(pcib) != pcib_get_domain(bus))
+		return;
 	upinfo = device_get_ivars(pcib);
 	if (upinfo->cfg.pcie.pcie_location == 0)
 		return;