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, 88 insertions, 0 deletions

diff --git a/drivers/usb/serial/wishbone-serial.c b/drivers/usb/serial/wishbone-serial.c
new file mode 100644
index 000000000..4a1fed4cb
--- /dev/null
+++ b/drivers/usb/serial/wishbone-serial.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * USB Wishbone-Serial adapter driver
+ *
+ * Copyright (C) 2013 Wesley W. Terpstra <w.terpstra@gsi.de>
+ * Copyright (C) 2013 GSI Helmholtz Centre for Heavy Ion Research GmbH
+ */
+
+#include <linux/kernel.h>
+#include <linux/tty.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+#define GSI_VENDOR_OPENCLOSE 0xB0
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE_AND_INTERFACE_INFO(0x1D50, 0x6062, 0xFF, 0xFF, 0xFF) },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+/*
+ * Etherbone must be told that a new stream has begun before data arrives.
+ * This is necessary to restart the negotiation of Wishbone bus parameters.
+ * Similarly, when the stream ends, Etherbone must be told so that the cycle
+ * line can be driven low in the case that userspace failed to do so.
+ */
+static int usb_gsi_openclose(struct usb_serial_port *port, int value)
+{
+	struct usb_device *dev = port->serial->dev;
+
+	return usb_control_msg(
+		dev,
+		usb_sndctrlpipe(dev, 0), /* Send to EP0OUT */
+		GSI_VENDOR_OPENCLOSE,
+		USB_DIR_OUT|USB_TYPE_VENDOR|USB_RECIP_INTERFACE,
+		value, /* wValue = device is open(1) or closed(0) */
+		port->serial->interface->cur_altsetting->desc.bInterfaceNumber,
+		NULL, 0,  /* There is no data stage */
+		5000); /* Timeout till operation fails */
+}
+
+static int wishbone_serial_open(struct tty_struct *tty,
+				struct usb_serial_port *port)
+{
+	int retval;
+
+	retval = usb_gsi_openclose(port, 1);
+	if (retval) {
+		dev_err(&port->serial->dev->dev,
+		       "Could not mark device as open (%d)\n",
+		       retval);
+		return retval;
+	}
+
+	retval = usb_serial_generic_open(tty, port);
+	if (retval)
+		usb_gsi_openclose(port, 0);
+
+	return retval;
+}
+
+static void wishbone_serial_close(struct usb_serial_port *port)
+{
+	usb_serial_generic_close(port);
+	usb_gsi_openclose(port, 0);
+}
+
+static struct usb_serial_driver wishbone_serial_device = {
+	.driver = {
+		.name =		"wishbone_serial",
+	},
+	.id_table =		id_table,
+	.num_ports =		1,
+	.open =			&wishbone_serial_open,
+	.close =		&wishbone_serial_close,
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&wishbone_serial_device, NULL
+};
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_AUTHOR("Wesley W. Terpstra <w.terpstra@gsi.de>");
+MODULE_DESCRIPTION("USB Wishbone-Serial adapter");
+MODULE_LICENSE("GPL");