KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.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");