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, 162 insertions, 0 deletions

diff --git a/drivers/acpi/acpi_lpit.c b/drivers/acpi/acpi_lpit.c
new file mode 100644
index 000000000..b8d98b1b4
--- /dev/null
+++ b/drivers/acpi/acpi_lpit.c
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * acpi_lpit.c - LPIT table processing functions
+ *
+ * Copyright (C) 2017 Intel Corporation. All rights reserved.
+ */
+
+#include <linux/cpu.h>
+#include <linux/acpi.h>
+#include <asm/msr.h>
+#include <asm/tsc.h>
+#include "internal.h"
+
+struct lpit_residency_info {
+	struct acpi_generic_address gaddr;
+	u64 frequency;
+	void __iomem *iomem_addr;
+};
+
+/* Storage for an memory mapped and FFH based entries */
+static struct lpit_residency_info residency_info_mem;
+static struct lpit_residency_info residency_info_ffh;
+
+static int lpit_read_residency_counter_us(u64 *counter, bool io_mem)
+{
+	int err;
+
+	if (io_mem) {
+		u64 count = 0;
+		int error;
+
+		error = acpi_os_read_iomem(residency_info_mem.iomem_addr, &count,
+					   residency_info_mem.gaddr.bit_width);
+		if (error)
+			return error;
+
+		*counter = div64_u64(count * 1000000ULL, residency_info_mem.frequency);
+		return 0;
+	}
+
+	err = rdmsrq_safe(residency_info_ffh.gaddr.address, counter);
+	if (!err) {
+		u64 mask = GENMASK_ULL(residency_info_ffh.gaddr.bit_offset +
+				       residency_info_ffh.gaddr. bit_width - 1,
+				       residency_info_ffh.gaddr.bit_offset);
+
+		*counter &= mask;
+		*counter >>= residency_info_ffh.gaddr.bit_offset;
+		*counter = div64_u64(*counter * 1000000ULL, residency_info_ffh.frequency);
+		return 0;
+	}
+
+	return -ENODATA;
+}
+
+static ssize_t low_power_idle_system_residency_us_show(struct device *dev,
+						       struct device_attribute *attr,
+						       char *buf)
+{
+	u64 counter;
+	int ret;
+
+	ret = lpit_read_residency_counter_us(&counter, true);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n", counter);
+}
+static DEVICE_ATTR_RO(low_power_idle_system_residency_us);
+
+static ssize_t low_power_idle_cpu_residency_us_show(struct device *dev,
+						    struct device_attribute *attr,
+						    char *buf)
+{
+	u64 counter;
+	int ret;
+
+	ret = lpit_read_residency_counter_us(&counter, false);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n", counter);
+}
+static DEVICE_ATTR_RO(low_power_idle_cpu_residency_us);
+
+int lpit_read_residency_count_address(u64 *address)
+{
+	if (!residency_info_mem.gaddr.address)
+		return -EINVAL;
+
+	*address = residency_info_mem.gaddr.address;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(lpit_read_residency_count_address);
+
+static void lpit_update_residency(struct lpit_residency_info *info,
+				 struct acpi_lpit_native *lpit_native)
+{
+	struct device *dev_root = bus_get_dev_root(&cpu_subsys);
+
+	/* Silently fail, if cpuidle attribute group is not present */
+	if (!dev_root)
+		return;
+
+	info->frequency = lpit_native->counter_frequency ?
+				lpit_native->counter_frequency : mul_u32_u32(tsc_khz, 1000U);
+	if (!info->frequency)
+		info->frequency = 1;
+
+	info->gaddr = lpit_native->residency_counter;
+	if (info->gaddr.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
+		info->iomem_addr = ioremap(info->gaddr.address,
+						   info->gaddr.bit_width / 8);
+		if (!info->iomem_addr)
+			goto exit;
+
+		sysfs_add_file_to_group(&dev_root->kobj,
+					&dev_attr_low_power_idle_system_residency_us.attr,
+					"cpuidle");
+	} else if (info->gaddr.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) {
+		sysfs_add_file_to_group(&dev_root->kobj,
+					&dev_attr_low_power_idle_cpu_residency_us.attr,
+					"cpuidle");
+	}
+exit:
+	put_device(dev_root);
+}
+
+static void lpit_process(u64 begin, u64 end)
+{
+	while (begin + sizeof(struct acpi_lpit_native) <= end) {
+		struct acpi_lpit_native *lpit_native = (struct acpi_lpit_native *)begin;
+
+		if (!lpit_native->header.type && !lpit_native->header.flags) {
+			if (lpit_native->residency_counter.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY &&
+			    !residency_info_mem.gaddr.address) {
+				lpit_update_residency(&residency_info_mem, lpit_native);
+			} else if (lpit_native->residency_counter.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE &&
+				   !residency_info_ffh.gaddr.address) {
+				lpit_update_residency(&residency_info_ffh, lpit_native);
+			}
+		}
+		begin += lpit_native->header.length;
+	}
+}
+
+void acpi_init_lpit(void)
+{
+	acpi_status status;
+	struct acpi_table_lpit *lpit;
+
+	status = acpi_get_table(ACPI_SIG_LPIT, 0, (struct acpi_table_header **)&lpit);
+	if (ACPI_FAILURE(status))
+		return;
+
+	lpit_process((u64)lpit + sizeof(*lpit),
+		     (u64)lpit + lpit->header.length);
+
+	acpi_put_table((struct acpi_table_header *)lpit);
+}