[PATCH v8 3/4] PCI: dwc: Add dw_pcie_mask_msi() to mask chained MSI without freeing domain

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

dw_pcie_free_msi() detaches the chained MSI handler(s) and then removes
the MSI IRQ domain via irq_domain_remove(). That is correct for the
dw_pcie_host_deinit() teardown path, where PCI devices have already been
removed and no MSI mappings remain.

It is not safe to call from the shutdown()/reboot path. device_shutdown()
does not remove PCI devices or tear down their per-device child MSI
domains, so endpoint drivers that do not free their MSI vectors in a
shutdown callback leave live MSI descriptors parented to the domain.
Removing the domain there orphans those descriptors and leaves dangling
references to freed memory: during a subsequent kexec CPU teardown, IRQ
migration walks irq_data->parent_data and can dereference the freed
msi_irq_domain.

Add dw_pcie_mask_msi(), which only disables the controller's chained MSI
parent interrupt line(s) to stop further MSI delivery, leaving the IRQ
domain and the downstream MSI mappings intact. This gives the shutdown
path a way to silence MSIs before clocks/power are cut without the
teardown side effects of dw_pcie_free_msi().

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 22 ++++++++++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.h      |  4 ++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 0837bb9e67e0..7f0126c5336b 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -240,6 +240,28 @@ void dw_pcie_free_msi(struct dw_pcie_rp *pp)
 }
 EXPORT_SYMBOL_GPL(dw_pcie_free_msi);
 
+/**
+ * dw_pcie_mask_msi - Mask the chained MSI parent interrupt(s)
+ * @pp: DWC PCIe RP private data
+ *
+ * Disable the controller's chained MSI interrupt line(s) to stop further
+ * MSI delivery, while leaving the MSI IRQ domain and the MSI mappings held
+ * by downstream devices intact. Unlike dw_pcie_free_msi(), this does not
+ * remove the IRQ domain, so it is safe to call from the shutdown()/reboot
+ * path where PCI devices are not removed and their MSI descriptors must not
+ * be orphaned.
+ */
+void dw_pcie_mask_msi(struct dw_pcie_rp *pp)
+{
+	u32 ctrl;
+
+	for (ctrl = 0; ctrl < MAX_MSI_CTRLS; ctrl++) {
+		if (pp->msi_irq[ctrl] > 0)
+			disable_irq(pp->msi_irq[ctrl]);
+	}
+}
+EXPORT_SYMBOL_GPL(dw_pcie_mask_msi);
+
 void dw_pcie_msi_init(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 90e6e25fde73..16b180275aca 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -866,6 +866,7 @@ void dw_handle_msi_irq(struct dw_pcie_rp *pp);
 void dw_pcie_msi_init(struct dw_pcie_rp *pp);
 int dw_pcie_msi_host_init(struct dw_pcie_rp *pp);
 void dw_pcie_free_msi(struct dw_pcie_rp *pp);
+void dw_pcie_mask_msi(struct dw_pcie_rp *pp);
 int dw_pcie_setup_rc(struct dw_pcie_rp *pp);
 int dw_pcie_host_init(struct dw_pcie_rp *pp);
 void dw_pcie_host_deinit(struct dw_pcie_rp *pp);
@@ -896,6 +897,9 @@ static inline int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 static inline void dw_pcie_free_msi(struct dw_pcie_rp *pp)
 { }
 
+static inline void dw_pcie_mask_msi(struct dw_pcie_rp *pp)
+{ }
+
 static inline int dw_pcie_setup_rc(struct dw_pcie_rp *pp)
 {
 	return 0;

-- 
2.34.1