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, 140 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-macsmc.c b/drivers/rtc/rtc-macsmc.c
new file mode 100644
index 000000000..8fe883066
--- /dev/null
+++ b/drivers/rtc/rtc-macsmc.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple SMC RTC driver
+ * Copyright The Asahi Linux Contributors
+ */
+
+#include <linux/bitops.h>
+#include <linux/mfd/macsmc.h>
+#include <linux/module.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+/* 48-bit RTC */
+#define RTC_BYTES 6
+#define RTC_BITS (8 * RTC_BYTES)
+
+/* 32768 Hz clock */
+#define RTC_SEC_SHIFT 15
+
+struct macsmc_rtc {
+	struct device *dev;
+	struct apple_smc *smc;
+	struct rtc_device *rtc_dev;
+	struct nvmem_cell *rtc_offset;
+};
+
+static int macsmc_rtc_get_time(struct device *dev, struct rtc_time *tm)
+{
+	struct macsmc_rtc *rtc = dev_get_drvdata(dev);
+	u64 ctr = 0, off = 0;
+	time64_t now;
+	void *p_off;
+	size_t len;
+	int ret;
+
+	ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
+	if (ret < 0)
+		return ret;
+	if (ret != RTC_BYTES)
+		return -EIO;
+
+	p_off = nvmem_cell_read(rtc->rtc_offset, &len);
+	if (IS_ERR(p_off))
+		return PTR_ERR(p_off);
+	if (len < RTC_BYTES) {
+		kfree(p_off);
+		return -EIO;
+	}
+
+	memcpy(&off, p_off, RTC_BYTES);
+	kfree(p_off);
+
+	/* Sign extend from 48 to 64 bits, then arithmetic shift right 15 bits to get seconds */
+	now = sign_extend64(ctr + off, RTC_BITS - 1) >> RTC_SEC_SHIFT;
+	rtc_time64_to_tm(now, tm);
+
+	return ret;
+}
+
+static int macsmc_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct macsmc_rtc *rtc = dev_get_drvdata(dev);
+	u64 ctr = 0, off = 0;
+	int ret;
+
+	ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
+	if (ret < 0)
+		return ret;
+	if (ret != RTC_BYTES)
+		return -EIO;
+
+	/* This sets the offset such that the set second begins now */
+	off = (rtc_tm_to_time64(tm) << RTC_SEC_SHIFT) - ctr;
+	return nvmem_cell_write(rtc->rtc_offset, &off, RTC_BYTES);
+}
+
+static const struct rtc_class_ops macsmc_rtc_ops = {
+	.read_time = macsmc_rtc_get_time,
+	.set_time = macsmc_rtc_set_time,
+};
+
+static int macsmc_rtc_probe(struct platform_device *pdev)
+{
+	struct apple_smc *smc = dev_get_drvdata(pdev->dev.parent);
+	struct macsmc_rtc *rtc;
+
+	/*
+	 * MFD will probe this device even without a node in the device tree,
+	 * thus bail out early if the SMC on the current machines does not
+	 * support RTC and has no node in the device tree.
+	 */
+	if (!pdev->dev.of_node)
+		return -ENODEV;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->dev = &pdev->dev;
+	rtc->smc = smc;
+
+	rtc->rtc_offset = devm_nvmem_cell_get(&pdev->dev, "rtc_offset");
+	if (IS_ERR(rtc->rtc_offset))
+		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->rtc_offset),
+				     "Failed to get rtc_offset NVMEM cell\n");
+
+	rtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtc_dev))
+		return PTR_ERR(rtc->rtc_dev);
+
+	rtc->rtc_dev->ops = &macsmc_rtc_ops;
+	rtc->rtc_dev->range_min = S64_MIN >> (RTC_SEC_SHIFT + (64 - RTC_BITS));
+	rtc->rtc_dev->range_max = S64_MAX >> (RTC_SEC_SHIFT + (64 - RTC_BITS));
+
+	platform_set_drvdata(pdev, rtc);
+
+	return devm_rtc_register_device(rtc->rtc_dev);
+}
+
+static const struct of_device_id macsmc_rtc_of_table[] = {
+	{ .compatible = "apple,smc-rtc", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, macsmc_rtc_of_table);
+
+static struct platform_driver macsmc_rtc_driver = {
+	.driver = {
+		.name = "macsmc-rtc",
+		.of_match_table = macsmc_rtc_of_table,
+	},
+	.probe = macsmc_rtc_probe,
+};
+module_platform_driver(macsmc_rtc_driver);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_DESCRIPTION("Apple SMC RTC driver");
+MODULE_AUTHOR("Hector Martin <marcan@marcan.st>");