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, 256 insertions, 0 deletions

diff --git a/drivers/thunderbolt/cap.c b/drivers/thunderbolt/cap.c
new file mode 100644
index 000000000..4ab22d529
--- /dev/null
+++ b/drivers/thunderbolt/cap.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Thunderbolt driver - capabilities lookup
+ *
+ * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
+ * Copyright (C) 2018, Intel Corporation
+ */
+
+#include <linux/slab.h>
+#include <linux/errno.h>
+
+#include "tb.h"
+
+#define CAP_OFFSET_MAX		0xff
+#define VSE_CAP_OFFSET_MAX	0xffff
+#define TMU_ACCESS_EN		BIT(20)
+
+static int tb_port_enable_tmu(struct tb_port *port, bool enable)
+{
+	struct tb_switch *sw = port->sw;
+	u32 value, offset;
+	int ret;
+
+	/*
+	 * Legacy devices need to have TMU access enabled before port
+	 * space can be fully accessed.
+	 */
+	if (tb_switch_is_light_ridge(sw))
+		offset = 0x26;
+	else if (tb_switch_is_eagle_ridge(sw))
+		offset = 0x2a;
+	else
+		return 0;
+
+	ret = tb_sw_read(sw, &value, TB_CFG_SWITCH, offset, 1);
+	if (ret)
+		return ret;
+
+	if (enable)
+		value |= TMU_ACCESS_EN;
+	else
+		value &= ~TMU_ACCESS_EN;
+
+	return tb_sw_write(sw, &value, TB_CFG_SWITCH, offset, 1);
+}
+
+static void tb_port_dummy_read(struct tb_port *port)
+{
+	/*
+	 * When reading from next capability pointer location in port
+	 * config space the read data is not cleared on LR. To avoid
+	 * reading stale data on next read perform one dummy read after
+	 * port capabilities are walked.
+	 */
+	if (tb_switch_is_light_ridge(port->sw)) {
+		u32 dummy;
+
+		tb_port_read(port, &dummy, TB_CFG_PORT, 0, 1);
+	}
+}
+
+/**
+ * tb_port_next_cap() - Return next capability in the linked list
+ * @port: Port to find the capability for
+ * @offset: Previous capability offset (%0 for start)
+ *
+ * Finds dword offset of the next capability in port config space
+ * capability list. When passed %0 in @offset parameter, first entry
+ * will be returned, if it exists.
+ *
+ * Return:
+ * * Double word offset of the first or next capability - On success.
+ * * %0 - If no next capability is found.
+ * * Negative errno - Another error occurred.
+ */
+int tb_port_next_cap(struct tb_port *port, unsigned int offset)
+{
+	struct tb_cap_any header;
+	int ret;
+
+	if (!offset)
+		return port->config.first_cap_offset;
+
+	ret = tb_port_read(port, &header, TB_CFG_PORT, offset, 1);
+	if (ret)
+		return ret;
+
+	return header.basic.next;
+}
+
+static int __tb_port_find_cap(struct tb_port *port, enum tb_port_cap cap)
+{
+	int offset = 0;
+
+	do {
+		struct tb_cap_any header;
+		int ret;
+
+		offset = tb_port_next_cap(port, offset);
+		if (offset < 0)
+			return offset;
+
+		ret = tb_port_read(port, &header, TB_CFG_PORT, offset, 1);
+		if (ret)
+			return ret;
+
+		if (header.basic.cap == cap)
+			return offset;
+	} while (offset > 0);
+
+	return -ENOENT;
+}
+
+/**
+ * tb_port_find_cap() - Find port capability
+ * @port: Port to find the capability for
+ * @cap: Capability to look
+ *
+ * Return:
+ * * Offset to the start of capability - On success.
+ * * %-ENOENT - If no such capability was found.
+ * * Negative errno - Another error occurred.
+ */
+int tb_port_find_cap(struct tb_port *port, enum tb_port_cap cap)
+{
+	int ret;
+
+	ret = tb_port_enable_tmu(port, true);
+	if (ret)
+		return ret;
+
+	ret = __tb_port_find_cap(port, cap);
+
+	tb_port_dummy_read(port);
+	tb_port_enable_tmu(port, false);
+
+	return ret;
+}
+
+/**
+ * tb_switch_next_cap() - Return next capability in the linked list
+ * @sw: Switch to find the capability for
+ * @offset: Previous capability offset (%0 for start)
+ *
+ * Finds dword offset of the next capability in port config space
+ * capability list. When passed %0 in @offset parameter, first entry
+ * will be returned, if it exists.
+ *
+ * Return:
+ * * Double word offset of the first or next capability - On success.
+ * * %0 - If no next capability is found.
+ * * Negative errno - Another error occurred.
+ */
+int tb_switch_next_cap(struct tb_switch *sw, unsigned int offset)
+{
+	struct tb_cap_any header;
+	int ret;
+
+	if (!offset)
+		return sw->config.first_cap_offset;
+
+	ret = tb_sw_read(sw, &header, TB_CFG_SWITCH, offset, 2);
+	if (ret)
+		return ret;
+
+	switch (header.basic.cap) {
+	case TB_SWITCH_CAP_TMU:
+		ret = header.basic.next;
+		break;
+
+	case TB_SWITCH_CAP_VSE:
+		if (!header.extended_short.length)
+			ret = header.extended_long.next;
+		else
+			ret = header.extended_short.next;
+		break;
+
+	default:
+		tb_sw_dbg(sw, "unknown capability %#x at %#x\n",
+			  header.basic.cap, offset);
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret >= VSE_CAP_OFFSET_MAX ? 0 : ret;
+}
+
+/**
+ * tb_switch_find_cap() - Find switch capability
+ * @sw: Switch to find the capability for
+ * @cap: Capability to look
+ *
+ * Return:
+ * * Offset to the start of capability - On success.
+ * * %-ENOENT - If no such capability was found.
+ * * Negative errno - Another error occurred.
+ */
+int tb_switch_find_cap(struct tb_switch *sw, enum tb_switch_cap cap)
+{
+	int offset = 0;
+
+	do {
+		struct tb_cap_any header;
+		int ret;
+
+		offset = tb_switch_next_cap(sw, offset);
+		if (offset < 0)
+			return offset;
+
+		ret = tb_sw_read(sw, &header, TB_CFG_SWITCH, offset, 1);
+		if (ret)
+			return ret;
+
+		if (header.basic.cap == cap)
+			return offset;
+	} while (offset);
+
+	return -ENOENT;
+}
+
+/**
+ * tb_switch_find_vse_cap() - Find switch vendor specific capability
+ * @sw: Switch to find the capability for
+ * @vsec: Vendor specific capability to look
+ *
+ * This function enumerates vendor specific capabilities (VSEC) of a
+ * switch and returns offset when capability matching @vsec is found.
+ *
+ * Return:
+ * * Offset of capability - On success.
+ * * %-ENOENT - If capability was not found.
+ * * Negative errno - Another error occurred.
+ */
+int tb_switch_find_vse_cap(struct tb_switch *sw, enum tb_switch_vse_cap vsec)
+{
+	int offset = 0;
+
+	do {
+		struct tb_cap_any header;
+		int ret;
+
+		offset = tb_switch_next_cap(sw, offset);
+		if (offset < 0)
+			return offset;
+
+		ret = tb_sw_read(sw, &header, TB_CFG_SWITCH, offset, 1);
+		if (ret)
+			return ret;
+
+		if (header.extended_short.cap == TB_SWITCH_CAP_VSE &&
+		    header.extended_short.vsec_id == vsec)
+			return offset;
+	} while (offset);
+
+	return -ENOENT;
+}