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, 191 insertions, 0 deletions

diff --git a/drivers/usb/serial/symbolserial.c b/drivers/usb/serial/symbolserial.c
new file mode 100644
index 000000000..8823671a9
--- /dev/null
+++ b/drivers/usb/serial/symbolserial.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Symbol USB barcode to serial driver
+ *
+ * Copyright (C) 2013 Johan Hovold <jhovold@gmail.com>
+ * Copyright (C) 2009 Greg Kroah-Hartman <gregkh@suse.de>
+ * Copyright (C) 2009 Novell Inc.
+ */
+
+#include <linux/kernel.h>
+#include <linux/tty.h>
+#include <linux/slab.h>
+#include <linux/tty_flip.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(0x05e0, 0x0600) },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+struct symbol_private {
+	spinlock_t lock;	/* protects the following flags */
+	bool throttled;
+	bool actually_throttled;
+};
+
+static void symbol_int_callback(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	struct symbol_private *priv = usb_get_serial_port_data(port);
+	unsigned char *data = urb->transfer_buffer;
+	int status = urb->status;
+	unsigned long flags;
+	int result;
+	int data_length;
+
+	switch (status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n",
+			__func__, status);
+		return;
+	default:
+		dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n",
+			__func__, status);
+		goto exit;
+	}
+
+	usb_serial_debug_data(&port->dev, __func__, urb->actual_length, data);
+
+	/*
+	 * Data from the device comes with a 1 byte header:
+	 *
+	 * <size of data> <data>...
+	 */
+	if (urb->actual_length > 1) {
+		data_length = data[0];
+		if (data_length > (urb->actual_length - 1))
+			data_length = urb->actual_length - 1;
+		tty_insert_flip_string(&port->port, &data[1], data_length);
+		tty_flip_buffer_push(&port->port);
+	} else {
+		dev_dbg(&port->dev, "%s - short packet\n", __func__);
+	}
+
+exit:
+	spin_lock_irqsave(&priv->lock, flags);
+
+	/* Continue trying to always read if we should */
+	if (!priv->throttled) {
+		result = usb_submit_urb(port->interrupt_in_urb, GFP_ATOMIC);
+		if (result)
+			dev_err(&port->dev,
+			    "%s - failed resubmitting read urb, error %d\n",
+							__func__, result);
+	} else
+		priv->actually_throttled = true;
+	spin_unlock_irqrestore(&priv->lock, flags);
+}
+
+static int symbol_open(struct tty_struct *tty, struct usb_serial_port *port)
+{
+	struct symbol_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+	int result = 0;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	priv->throttled = false;
+	priv->actually_throttled = false;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	/* Start reading from the device */
+	result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
+	if (result)
+		dev_err(&port->dev,
+			"%s - failed resubmitting read urb, error %d\n",
+			__func__, result);
+	return result;
+}
+
+static void symbol_close(struct usb_serial_port *port)
+{
+	usb_kill_urb(port->interrupt_in_urb);
+}
+
+static void symbol_throttle(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct symbol_private *priv = usb_get_serial_port_data(port);
+
+	spin_lock_irq(&priv->lock);
+	priv->throttled = true;
+	spin_unlock_irq(&priv->lock);
+}
+
+static void symbol_unthrottle(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct symbol_private *priv = usb_get_serial_port_data(port);
+	int result;
+	bool was_throttled;
+
+	spin_lock_irq(&priv->lock);
+	priv->throttled = false;
+	was_throttled = priv->actually_throttled;
+	priv->actually_throttled = false;
+	spin_unlock_irq(&priv->lock);
+
+	if (was_throttled) {
+		result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
+		if (result)
+			dev_err(&port->dev,
+				"%s - failed submitting read urb, error %d\n",
+							__func__, result);
+	}
+}
+
+static int symbol_port_probe(struct usb_serial_port *port)
+{
+	struct symbol_private *priv;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return -ENOMEM;
+
+	spin_lock_init(&priv->lock);
+
+	usb_set_serial_port_data(port, priv);
+
+	return 0;
+}
+
+static void symbol_port_remove(struct usb_serial_port *port)
+{
+	struct symbol_private *priv = usb_get_serial_port_data(port);
+
+	kfree(priv);
+}
+
+static struct usb_serial_driver symbol_device = {
+	.driver = {
+		.name =		"symbol",
+	},
+	.id_table =		id_table,
+	.num_ports =		1,
+	.num_interrupt_in =	1,
+	.port_probe =		symbol_port_probe,
+	.port_remove =		symbol_port_remove,
+	.open =			symbol_open,
+	.close =		symbol_close,
+	.throttle = 		symbol_throttle,
+	.unthrottle =		symbol_unthrottle,
+	.read_int_callback =	symbol_int_callback,
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&symbol_device, NULL
+};
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_DESCRIPTION("Symbol USB barcode to serial driver");
+MODULE_LICENSE("GPL v2");