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, 177 insertions, 0 deletions

diff --git a/drivers/usb/serial/omninet.c b/drivers/usb/serial/omninet.c
new file mode 100644
index 000000000..363b8432c
--- /dev/null
+++ b/drivers/usb/serial/omninet.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * USB ZyXEL omni.net driver
+ *
+ * Copyright (C) 2013,2017 Johan Hovold <johan@kernel.org>
+ *
+ * See Documentation/usb/usb-serial.rst for more information on using this
+ * driver
+ *
+ * Please report both successes and troubles to the author at omninet@kroah.com
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+#define DRIVER_AUTHOR "Alessandro Zummo"
+#define DRIVER_DESC "USB ZyXEL omni.net Driver"
+
+#define ZYXEL_VENDOR_ID		0x0586
+#define ZYXEL_OMNINET_ID	0x1000
+#define ZYXEL_OMNI_56K_PLUS_ID	0x1500
+/* This one seems to be a re-branded ZyXEL device */
+#define BT_IGNITIONPRO_ID	0x2000
+
+#define OMNINET_HEADERLEN	4
+#define OMNINET_BULKOUTSIZE	64
+#define OMNINET_PAYLOADSIZE	(OMNINET_BULKOUTSIZE - OMNINET_HEADERLEN)
+
+/* function prototypes */
+static void omninet_process_read_urb(struct urb *urb);
+static int omninet_prepare_write_buffer(struct usb_serial_port *port,
+				void *buf, size_t count);
+static int omninet_calc_num_ports(struct usb_serial *serial,
+				struct usb_serial_endpoints *epds);
+static int omninet_port_probe(struct usb_serial_port *port);
+static void omninet_port_remove(struct usb_serial_port *port);
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(ZYXEL_VENDOR_ID, ZYXEL_OMNINET_ID) },
+	{ USB_DEVICE(ZYXEL_VENDOR_ID, ZYXEL_OMNI_56K_PLUS_ID) },
+	{ USB_DEVICE(ZYXEL_VENDOR_ID, BT_IGNITIONPRO_ID) },
+	{ }						/* Terminating entry */
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+static struct usb_serial_driver zyxel_omninet_device = {
+	.driver = {
+		.name =		"omninet",
+	},
+	.description =		"ZyXEL - omni.net usb",
+	.id_table =		id_table,
+	.num_bulk_out =		2,
+	.bulk_out_size =	OMNINET_BULKOUTSIZE,
+	.calc_num_ports =	omninet_calc_num_ports,
+	.port_probe =		omninet_port_probe,
+	.port_remove =		omninet_port_remove,
+	.process_read_urb =	omninet_process_read_urb,
+	.prepare_write_buffer =	omninet_prepare_write_buffer,
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&zyxel_omninet_device, NULL
+};
+
+
+/*
+ * The protocol.
+ *
+ * The omni.net always exchange 64 bytes of data with the host. The first
+ * four bytes are the control header.
+ *
+ * oh_seq is a sequence number. Don't know if/how it's used.
+ * oh_len is the length of the data bytes in the packet.
+ * oh_xxx Bit-mapped, related to handshaking and status info.
+ *	I normally set it to 0x03 in transmitted frames.
+ *	7: Active when the TA is in a CONNECTed state.
+ *	6: unknown
+ *	5: handshaking, unknown
+ *	4: handshaking, unknown
+ *	3: unknown, usually 0
+ *	2: unknown, usually 0
+ *	1: handshaking, unknown, usually set to 1 in transmitted frames
+ *	0: handshaking, unknown, usually set to 1 in transmitted frames
+ * oh_pad Probably a pad byte.
+ *
+ * After the header you will find data bytes if oh_len was greater than zero.
+ */
+struct omninet_header {
+	__u8	oh_seq;
+	__u8	oh_len;
+	__u8	oh_xxx;
+	__u8	oh_pad;
+};
+
+struct omninet_data {
+	__u8	od_outseq;	/* Sequence number for bulk_out URBs */
+};
+
+static int omninet_calc_num_ports(struct usb_serial *serial,
+					struct usb_serial_endpoints *epds)
+{
+	/* We need only the second bulk-out for our single-port device. */
+	epds->bulk_out[0] = epds->bulk_out[1];
+	epds->num_bulk_out = 1;
+
+	return 1;
+}
+
+static int omninet_port_probe(struct usb_serial_port *port)
+{
+	struct omninet_data *od;
+
+	od = kzalloc_obj(*od);
+	if (!od)
+		return -ENOMEM;
+
+	usb_set_serial_port_data(port, od);
+
+	return 0;
+}
+
+static void omninet_port_remove(struct usb_serial_port *port)
+{
+	struct omninet_data *od;
+
+	od = usb_get_serial_port_data(port);
+	kfree(od);
+}
+
+static void omninet_process_read_urb(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	const struct omninet_header *hdr = urb->transfer_buffer;
+	const unsigned char *data;
+	size_t data_len;
+
+	if (urb->actual_length <= OMNINET_HEADERLEN || !hdr->oh_len)
+		return;
+
+	data = (char *)urb->transfer_buffer + OMNINET_HEADERLEN;
+	data_len = min_t(size_t, urb->actual_length - OMNINET_HEADERLEN,
+								hdr->oh_len);
+	tty_insert_flip_string(&port->port, data, data_len);
+	tty_flip_buffer_push(&port->port);
+}
+
+static int omninet_prepare_write_buffer(struct usb_serial_port *port,
+					void *buf, size_t count)
+{
+	struct omninet_data *od = usb_get_serial_port_data(port);
+	struct omninet_header *header = buf;
+
+	count = min_t(size_t, count, OMNINET_PAYLOADSIZE);
+
+	count = kfifo_out_locked(&port->write_fifo, buf + OMNINET_HEADERLEN,
+			count, &port->lock);
+
+	header->oh_seq = od->od_outseq++;
+	header->oh_len = count;
+	header->oh_xxx = 0x03;
+	header->oh_pad = 0x00;
+
+	/* always 64 bytes */
+	return OMNINET_BULKOUTSIZE;
+}
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL v2");