[RFC PATCH v2 19/22] RFC: pci: Add BUS_NOTIFY_PCI_BUS_MASTER event

[Alexey Kardashevskiy <aik@amd.com>]

TDISP allows secure MMIO access to a validated MMIO range.
The validation is done in the TSM and after that point changing
the device's Memory Space enable (MSE) or Bus Master enable (BME)
transitions the device into the error state.

For PCI device drivers which enable MSE, then BME, and then
start using the device, enabling BME is a logical point to perform
the MMIO range validation in the TSM.

Define new event for a bus. TSM is going to listen to it in the TVM
and do the validation for TEE ranges.

This does not switch MMIO to private by default though as this is
for the driver to decide (at least, for now).

Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
---
 include/linux/device/bus.h          |  3 ++
 drivers/pci/pci.c                   |  3 ++
 drivers/virt/coco/guest/tsm-guest.c | 35 ++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index f5a56efd2bd6..12f46ca69239 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -278,8 +278,11 @@ enum bus_notifier_event {
 	BUS_NOTIFY_UNBIND_DRIVER,
 	BUS_NOTIFY_UNBOUND_DRIVER,
 	BUS_NOTIFY_DRIVER_NOT_BOUND,
+	BUS_NOTIFY_PCI_BUS_MASTER,
 };
 
+void bus_notify(struct device *dev, enum bus_notifier_event value);
+
 struct kset *bus_get_kset(const struct bus_type *bus);
 struct device *bus_get_dev_root(const struct bus_type *bus);
 
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b462bab597f7..3aeaa583cd92 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4294,6 +4294,9 @@ static void __pci_set_master(struct pci_dev *dev, bool enable)
 		pci_write_config_word(dev, PCI_COMMAND, cmd);
 	}
 	dev->is_busmaster = enable;
+
+	if (enable)
+		bus_notify(&dev->dev, BUS_NOTIFY_PCI_BUS_MASTER);
 }
 
 /**
diff --git a/drivers/virt/coco/guest/tsm-guest.c b/drivers/virt/coco/guest/tsm-guest.c
index d3be089308e0..d30e49c154e0 100644
--- a/drivers/virt/coco/guest/tsm-guest.c
+++ b/drivers/virt/coco/guest/tsm-guest.c
@@ -2,6 +2,7 @@
 
 #include <linux/module.h>
 #include <linux/tsm.h>
+#include <linux/pci.h>
 
 #define DRIVER_VERSION	"0.1"
 #define DRIVER_AUTHOR	"aik@amd.com"
@@ -241,6 +242,36 @@ static const struct attribute_group tdi_group = {
 	.attrs = tdi_attrs,
 };
 
+/* In case BUS_NOTIFY_PCI_BUS_MASTER is no good, a driver can call pci_dev_tdi_validate() */
+int pci_dev_tdi_validate(struct pci_dev *pdev, bool invalidate)
+{
+	struct tsm_tdi *tdi = tsm_tdi_get(&pdev->dev);
+	int ret;
+
+	if (!tdi)
+		return -EFAULT;
+
+	ret = tsm_tdi_validate(tdi, TDI_VALIDATE_DMA | TDI_VALIDATE_MMIO, invalidate);
+
+	tsm_tdi_put(tdi);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_dev_tdi_validate);
+
+static int tsm_guest_pci_bus_notifier(struct notifier_block *nb, unsigned long action, void *data)
+{
+	switch (action) {
+	case BUS_NOTIFY_UNBOUND_DRIVER:
+		pci_dev_tdi_validate(to_pci_dev(data), true);
+		break;
+	case BUS_NOTIFY_PCI_BUS_MASTER:
+		pci_dev_tdi_validate(to_pci_dev(data), false);
+		break;
+	}
+
+	return NOTIFY_OK;
+}
+
 struct tsm_guest_subsys *tsm_guest_register(struct device *parent,
 					    struct tsm_vm_ops *vmops,
 					    void *private_data)
@@ -258,12 +289,16 @@ struct tsm_guest_subsys *tsm_guest_register(struct device *parent,
 	gsubsys->ops = vmops;
 	gsubsys->private_data = private_data;
 
+	gsubsys->notifier.notifier_call = tsm_guest_pci_bus_notifier;
+	bus_register_notifier(&pci_bus_type, &gsubsys->notifier);
+
 	return gsubsys;
 }
 EXPORT_SYMBOL_GPL(tsm_guest_register);
 
 void tsm_guest_unregister(struct tsm_guest_subsys *gsubsys)
 {
+	bus_unregister_notifier(&pci_bus_type, &gsubsys->notifier);
 	tsm_unregister(&gsubsys->base);
 }
 EXPORT_SYMBOL_GPL(tsm_guest_unregister);
-- 
2.47.1