The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 6cff20ce3b92ffbf2fc5eb9e5a030b3672aa414a # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025081509-uncrown-janitor-adad@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 6cff20ce3b92ffbf2fc5eb9e5a030b3672aa414a Mon Sep 17 00:00:00 2001 From: Lukas Wunner lukas@wunner.de Date: Sun, 13 Jul 2025 16:31:01 +0200 Subject: [PATCH] PCI/ACPI: Fix runtime PM ref imbalance on Hot-Plug Capable ports
pci_bridge_d3_possible() is called from both pcie_portdrv_probe() and pcie_portdrv_remove() to determine whether runtime power management shall be enabled (on probe) or disabled (on remove) on a PCIe port.
The underlying assumption is that pci_bridge_d3_possible() always returns the same value, else a runtime PM reference imbalance would occur. That assumption is not given if the PCIe port is inaccessible on remove due to hot-unplug: pci_bridge_d3_possible() calls pciehp_is_native(), which accesses Config Space to determine whether the port is Hot-Plug Capable. An inaccessible port returns "all ones", which is converted to "all zeroes" by pcie_capability_read_dword(). Hence the port no longer seems Hot-Plug Capable on remove even though it was on probe.
The resulting runtime PM ref imbalance causes warning messages such as:
pcieport 0000:02:04.0: Runtime PM usage count underflow!
Avoid the Config Space access (and thus the runtime PM ref imbalance) by caching the Hot-Plug Capable bit in struct pci_dev.
The struct already contains an "is_hotplug_bridge" flag, which however is not only set on Hot-Plug Capable PCIe ports, but also Conventional PCI Hot-Plug bridges and ACPI slots. The flag identifies bridges which are allocated additional MMIO and bus number resources to allow for hierarchy expansion.
The kernel is somewhat sloppily using "is_hotplug_bridge" in a number of places to identify Hot-Plug Capable PCIe ports, even though the flag encompasses other devices. Subsequent commits replace these occurrences with the new flag to clearly delineate Hot-Plug Capable PCIe ports from other kinds of hotplug bridges.
Document the existing "is_hotplug_bridge" and the new "is_pciehp" flag and document the (non-obvious) requirement that pci_bridge_d3_possible() always returns the same value across the entire lifetime of a bridge, including its hot-removal.
Fixes: 5352a44a561d ("PCI: pciehp: Make pciehp_is_native() stricter") Reported-by: Laurent Bigonville bigon@bigon.be Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220216 Reported-by: Mario Limonciello mario.limonciello@amd.com Closes: https://lore.kernel.org/r/20250609020223.269407-3-superm1@kernel.org/ Link: https://lore.kernel.org/all/20250620025535.3425049-3-superm1@kernel.org/T/#u Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Bjorn Helgaas bhelgaas@google.com Acked-by: Rafael J. Wysocki rafael@kernel.org Cc: stable@vger.kernel.org # v4.18+ Link: https://patch.msgid.link/fe5dcc3b2e62ee1df7905d746bde161eb1b3291c.1752390101...
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c index b78e0e417324..efe478e5073e 100644 --- a/drivers/pci/pci-acpi.c +++ b/drivers/pci/pci-acpi.c @@ -816,13 +816,11 @@ int pci_acpi_program_hp_params(struct pci_dev *dev) bool pciehp_is_native(struct pci_dev *bridge) { const struct pci_host_bridge *host; - u32 slot_cap;
if (!IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE)) return false;
- pcie_capability_read_dword(bridge, PCI_EXP_SLTCAP, &slot_cap); - if (!(slot_cap & PCI_EXP_SLTCAP_HPC)) + if (!bridge->is_pciehp) return false;
if (pcie_ports_native) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index e9448d55113b..23d8fe98ddf9 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -3030,8 +3030,12 @@ static const struct dmi_system_id bridge_d3_blacklist[] = { * pci_bridge_d3_possible - Is it possible to put the bridge into D3 * @bridge: Bridge to check * - * This function checks if it is possible to move the bridge to D3. * Currently we only allow D3 for some PCIe ports and for Thunderbolt. + * + * Return: Whether it is possible to move the bridge to D3. + * + * The return value is guaranteed to be constant across the entire lifetime + * of the bridge, including its hot-removal. */ bool pci_bridge_d3_possible(struct pci_dev *bridge) { diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 4b8693ec9e4c..cf50be63bf5f 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -1678,7 +1678,7 @@ void set_pcie_hotplug_bridge(struct pci_dev *pdev)
pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, ®32); if (reg32 & PCI_EXP_SLTCAP_HPC) - pdev->is_hotplug_bridge = 1; + pdev->is_hotplug_bridge = pdev->is_pciehp = 1; }
static void set_pcie_thunderbolt(struct pci_dev *dev) diff --git a/include/linux/pci.h b/include/linux/pci.h index 05e68f35f392..d56d0dd80afb 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -328,6 +328,11 @@ struct rcec_ea; * determined (e.g., for Root Complex Integrated * Endpoints without the relevant Capability * Registers). + * @is_hotplug_bridge: Hotplug bridge of any kind (e.g. PCIe Hot-Plug Capable, + * Conventional PCI Hot-Plug, ACPI slot). + * Such bridges are allocated additional MMIO and bus + * number resources to allow for hierarchy expansion. + * @is_pciehp: PCIe Hot-Plug Capable bridge. */ struct pci_dev { struct list_head bus_list; /* Node in per-bus list */ @@ -451,6 +456,7 @@ struct pci_dev { unsigned int is_physfn:1; unsigned int is_virtfn:1; unsigned int is_hotplug_bridge:1; + unsigned int is_pciehp:1; unsigned int shpc_managed:1; /* SHPC owned by shpchp */ unsigned int is_thunderbolt:1; /* Thunderbolt controller */ /*