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, 126 insertions, 0 deletions

diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
new file mode 100644
index 000000000..36be8e69f
--- /dev/null
+++ b/drivers/mfd/viperboard.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Nano River Technologies viperboard driver
+ *
+ *  This is the core driver for the viperboard. There are cell drivers
+ *  available for I2C, ADC and both GPIOs. SPI is not yet supported.
+ *  The drivers do not support all features the board exposes. See user
+ *  manual of the viperboard.
+ *
+ *  (C) 2012 by Lemonage GmbH
+ *  Author: Lars Poeschel <poeschel@lemonage.de>
+ *  All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/mutex.h>
+
+#include <linux/mfd/core.h>
+#include <linux/mfd/viperboard.h>
+
+#include <linux/usb.h>
+
+
+static const struct usb_device_id vprbrd_table[] = {
+	{ USB_DEVICE(0x2058, 0x1005) },   /* Nano River Technologies */
+	{ }                               /* Terminating entry */
+};
+
+MODULE_DEVICE_TABLE(usb, vprbrd_table);
+
+static const struct mfd_cell vprbrd_devs[] = {
+	{
+		.name = "viperboard-gpio",
+	},
+	{
+		.name = "viperboard-i2c",
+	},
+	{
+		.name = "viperboard-adc",
+	},
+};
+
+static int vprbrd_probe(struct usb_interface *interface,
+			      const struct usb_device_id *id)
+{
+	struct vprbrd *vb;
+
+	u16 version = 0;
+	int pipe, ret;
+
+	/* allocate memory for our device state and initialize it */
+	vb = kzalloc_obj(*vb);
+	if (!vb)
+		return -ENOMEM;
+
+	mutex_init(&vb->lock);
+
+	vb->usb_dev = interface_to_usbdev(interface);
+
+	/* save our data pointer in this interface device */
+	usb_set_intfdata(interface, vb);
+	dev_set_drvdata(&vb->pdev.dev, vb);
+
+	/* get version information, major first, minor then */
+	pipe = usb_rcvctrlpipe(vb->usb_dev, 0);
+	ret = usb_control_msg(vb->usb_dev, pipe, VPRBRD_USB_REQUEST_MAJOR,
+		VPRBRD_USB_TYPE_IN, 0x0000, 0x0000, vb->buf, 1,
+		VPRBRD_USB_TIMEOUT_MS);
+	if (ret == 1)
+		version = vb->buf[0];
+
+	ret = usb_control_msg(vb->usb_dev, pipe, VPRBRD_USB_REQUEST_MINOR,
+		VPRBRD_USB_TYPE_IN, 0x0000, 0x0000, vb->buf, 1,
+		VPRBRD_USB_TIMEOUT_MS);
+	if (ret == 1) {
+		version <<= 8;
+		version = version | vb->buf[0];
+	}
+
+	dev_info(&interface->dev,
+		 "version %x.%02x found at bus %03d address %03d\n",
+		 version >> 8, version & 0xff,
+		 vb->usb_dev->bus->busnum, vb->usb_dev->devnum);
+
+	ret = mfd_add_hotplug_devices(&interface->dev, vprbrd_devs,
+				      ARRAY_SIZE(vprbrd_devs));
+	if (ret != 0) {
+		dev_err(&interface->dev, "Failed to add mfd devices to core.");
+		goto error;
+	}
+
+	return 0;
+
+error:
+	kfree(vb);
+
+	return ret;
+}
+
+static void vprbrd_disconnect(struct usb_interface *interface)
+{
+	struct vprbrd *vb = usb_get_intfdata(interface);
+
+	mfd_remove_devices(&interface->dev);
+	usb_set_intfdata(interface, NULL);
+	kfree(vb);
+
+	dev_dbg(&interface->dev, "disconnected\n");
+}
+
+static struct usb_driver vprbrd_driver = {
+	.name		= "viperboard",
+	.probe		= vprbrd_probe,
+	.disconnect	= vprbrd_disconnect,
+	.id_table	= vprbrd_table,
+};
+
+module_usb_driver(vprbrd_driver);
+
+MODULE_DESCRIPTION("Nano River Technologies viperboard mfd core driver");
+MODULE_AUTHOR("Lars Poeschel <poeschel@lemonage.de>");
+MODULE_LICENSE("GPL");