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, 112 insertions, 0 deletions

diff --git a/drivers/hid/hid-pxrc.c b/drivers/hid/hid-pxrc.c
new file mode 100644
index 000000000..71fe0c06d
--- /dev/null
+++ b/drivers/hid/hid-pxrc.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * HID driver for PhoenixRC 8-axis flight controller
+ *
+ * Copyright (C) 2022 Marcus Folkesson <marcus.folkesson@gmail.com>
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+struct pxrc_priv {
+	u8 slider;
+	u8 dial;
+	bool alternate;
+};
+
+static const __u8 pxrc_rdesc_fixed[] = {
+	0x05, 0x01,        // Usage Page (Generic Desktop Ctrls)
+	0x09, 0x04,        // Usage (Joystick)
+	0xA1, 0x01,        // Collection (Application)
+	0x09, 0x01,        //   Usage (Pointer)
+	0xA1, 0x00,        //   Collection (Physical)
+	0x09, 0x30,        //     Usage (X)
+	0x09, 0x36,        //     Usage (Slider)
+	0x09, 0x31,        //     Usage (Y)
+	0x09, 0x32,        //     Usage (Z)
+	0x09, 0x33,        //     Usage (Rx)
+	0x09, 0x34,        //     Usage (Ry)
+	0x09, 0x35,        //     Usage (Rz)
+	0x09, 0x37,        //     Usage (Dial)
+	0x15, 0x00,        //     Logical Minimum (0)
+	0x26, 0xFF, 0x00,  //     Logical Maximum (255)
+	0x35, 0x00,        //     Physical Minimum (0)
+	0x46, 0xFF, 0x00,  //     Physical Maximum (255)
+	0x75, 0x08,        //     Report Size (8)
+	0x95, 0x08,        //     Report Count (8)
+	0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
+	0xC0,              //   End Collection
+	0xC0,              // End Collection
+};
+
+static const __u8 *pxrc_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+				     unsigned int *rsize)
+{
+	hid_info(hdev, "fixing up PXRC report descriptor\n");
+	*rsize = sizeof(pxrc_rdesc_fixed);
+	return pxrc_rdesc_fixed;
+}
+
+static int pxrc_raw_event(struct hid_device *hdev, struct hid_report *report,
+	 u8 *data, int size)
+{
+	struct pxrc_priv *priv = hid_get_drvdata(hdev);
+
+	if (priv->alternate)
+		priv->slider = data[7];
+	else
+		priv->dial = data[7];
+
+	data[1] = priv->slider;
+	data[7] = priv->dial;
+
+	priv->alternate = !priv->alternate;
+	return 0;
+}
+
+static int pxrc_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret;
+	struct pxrc_priv *priv;
+
+	priv = devm_kzalloc(&hdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	hid_set_drvdata(hdev, priv);
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed\n");
+		return ret;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct hid_device_id pxrc_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_MULTIPLE_1781, USB_DEVICE_ID_PHOENIXRC) },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(hid, pxrc_devices);
+
+static struct hid_driver pxrc_driver = {
+	.name = "hid-pxrc",
+	.id_table = pxrc_devices,
+	.report_fixup = pxrc_report_fixup,
+	.probe = pxrc_probe,
+	.raw_event = pxrc_raw_event,
+};
+module_hid_driver(pxrc_driver);
+
+MODULE_AUTHOR("Marcus Folkesson <marcus.folkesson@gmail.com>");
+MODULE_DESCRIPTION("HID driver for PXRC 8-axis flight controller");
+MODULE_LICENSE("GPL");