KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 171 insertions, 0 deletions

diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
new file mode 100644
index 000000000..9e2a18c0b
--- /dev/null
+++ b/drivers/usb/serial/bus.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * USB Serial Converter Bus specific functions
+ *
+ * Copyright (C) 2002 Greg Kroah-Hartman (greg@kroah.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/tty.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+static int usb_serial_device_match(struct device *dev,
+				   const struct device_driver *drv)
+{
+	const struct usb_serial_port *port = to_usb_serial_port(dev);
+	const struct usb_serial_driver *driver = to_usb_serial_driver(drv);
+
+	/*
+	 * drivers are already assigned to ports in serial_probe so it's
+	 * a simple check here.
+	 */
+	if (driver == port->serial->type)
+		return 1;
+
+	return 0;
+}
+
+static int usb_serial_device_probe(struct device *dev)
+{
+	struct usb_serial_port *port = to_usb_serial_port(dev);
+	struct usb_serial_driver *driver;
+	struct device *tty_dev;
+	int retval = 0;
+	int minor;
+
+	/* make sure suspend/resume doesn't race against port_probe */
+	retval = usb_autopm_get_interface(port->serial->interface);
+	if (retval)
+		return retval;
+
+	driver = port->serial->type;
+	if (driver->port_probe) {
+		retval = driver->port_probe(port);
+		if (retval)
+			goto err_autopm_put;
+	}
+
+	minor = port->minor;
+	tty_dev = tty_port_register_device(&port->port, usb_serial_tty_driver,
+					   minor, dev);
+	if (IS_ERR(tty_dev)) {
+		retval = PTR_ERR(tty_dev);
+		goto err_port_remove;
+	}
+
+	usb_autopm_put_interface(port->serial->interface);
+
+	dev_info(&port->serial->dev->dev,
+		 "%s converter now attached to ttyUSB%d\n",
+		 driver->description, minor);
+
+	return 0;
+
+err_port_remove:
+	if (driver->port_remove)
+		driver->port_remove(port);
+err_autopm_put:
+	usb_autopm_put_interface(port->serial->interface);
+
+	return retval;
+}
+
+static void usb_serial_device_remove(struct device *dev)
+{
+	struct usb_serial_port *port = to_usb_serial_port(dev);
+	struct usb_serial_driver *driver;
+	int minor;
+	int autopm_err;
+
+	/*
+	 * Make sure suspend/resume doesn't race against port_remove.
+	 *
+	 * Note that no further runtime PM callbacks will be made if
+	 * autopm_get fails.
+	 */
+	autopm_err = usb_autopm_get_interface(port->serial->interface);
+
+	minor = port->minor;
+	tty_unregister_device(usb_serial_tty_driver, minor);
+
+	driver = port->serial->type;
+	if (driver->port_remove)
+		driver->port_remove(port);
+
+	dev_info(dev, "%s converter now disconnected from ttyUSB%d\n",
+		 driver->description, minor);
+
+	if (!autopm_err)
+		usb_autopm_put_interface(port->serial->interface);
+}
+
+static ssize_t new_id_store(struct device_driver *driver,
+			    const char *buf, size_t count)
+{
+	struct usb_serial_driver *usb_drv = to_usb_serial_driver(driver);
+	ssize_t retval = usb_store_new_id(&usb_drv->dynids, usb_drv->id_table,
+					 driver, buf, count);
+
+	if (retval >= 0 && usb_drv->usb_driver != NULL)
+		retval = usb_store_new_id(&usb_drv->usb_driver->dynids,
+					  usb_drv->usb_driver->id_table,
+					  &usb_drv->usb_driver->driver,
+					  buf, count);
+	return retval;
+}
+
+static ssize_t new_id_show(struct device_driver *driver, char *buf)
+{
+	struct usb_serial_driver *usb_drv = to_usb_serial_driver(driver);
+
+	return usb_show_dynids(&usb_drv->dynids, buf);
+}
+static DRIVER_ATTR_RW(new_id);
+
+static struct attribute *usb_serial_drv_attrs[] = {
+	&driver_attr_new_id.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(usb_serial_drv);
+
+static void free_dynids(struct usb_serial_driver *drv)
+{
+	struct usb_dynid *dynid, *n;
+
+	guard(mutex)(&usb_dynids_lock);
+	list_for_each_entry_safe(dynid, n, &drv->dynids.list, node) {
+		list_del(&dynid->node);
+		kfree(dynid);
+	}
+}
+
+const struct bus_type usb_serial_bus_type = {
+	.name =		"usb-serial",
+	.match =	usb_serial_device_match,
+	.probe =	usb_serial_device_probe,
+	.remove =	usb_serial_device_remove,
+	.drv_groups = 	usb_serial_drv_groups,
+};
+
+int usb_serial_bus_register(struct usb_serial_driver *driver)
+{
+	int retval;
+
+	driver->driver.bus = &usb_serial_bus_type;
+	INIT_LIST_HEAD(&driver->dynids.list);
+
+	retval = driver_register(&driver->driver);
+
+	return retval;
+}
+
+void usb_serial_bus_deregister(struct usb_serial_driver *driver)
+{
+	free_dynids(driver);
+	driver_unregister(&driver->driver);
+}
+