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, 99 insertions, 0 deletions

diff --git a/drivers/nvmem/u-boot-env.c b/drivers/nvmem/u-boot-env.c
new file mode 100644
index 000000000..467b28891
--- /dev/null
+++ b/drivers/nvmem/u-boot-env.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2022 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <linux/module.h>
+#include <linux/mtd/mtd.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#include "layouts/u-boot-env.h"
+
+struct u_boot_env {
+	struct device *dev;
+	struct nvmem_device *nvmem;
+	enum u_boot_env_format format;
+
+	struct mtd_info *mtd;
+};
+
+static int u_boot_env_read(void *context, unsigned int offset, void *val,
+			   size_t bytes)
+{
+	struct u_boot_env *priv = context;
+	struct device *dev = priv->dev;
+	size_t bytes_read;
+	int err;
+
+	err = mtd_read(priv->mtd, offset, bytes, &bytes_read, val);
+	if (err && !mtd_is_bitflip(err)) {
+		dev_err(dev, "Failed to read from mtd: %d\n", err);
+		return err;
+	}
+
+	if (bytes_read != bytes) {
+		dev_err(dev, "Failed to read %zu bytes\n", bytes);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int u_boot_env_probe(struct platform_device *pdev)
+{
+	struct nvmem_config config = {
+		.name = "u-boot-env",
+		.reg_read = u_boot_env_read,
+	};
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct u_boot_env *priv;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->dev = dev;
+
+	priv->format = (uintptr_t)of_device_get_match_data(dev);
+
+	priv->mtd = of_get_mtd_device_by_node(np);
+	if (IS_ERR(priv->mtd)) {
+		dev_err_probe(dev, PTR_ERR(priv->mtd), "Failed to get %pOF MTD\n", np);
+		return PTR_ERR(priv->mtd);
+	}
+
+	config.dev = dev;
+	config.priv = priv;
+	config.size = priv->mtd->size;
+
+	priv->nvmem = devm_nvmem_register(dev, &config);
+	if (IS_ERR(priv->nvmem))
+		return PTR_ERR(priv->nvmem);
+
+	return u_boot_env_parse(dev, priv->nvmem, priv->format);
+}
+
+static const struct of_device_id u_boot_env_of_match_table[] = {
+	{ .compatible = "u-boot,env", .data = (void *)U_BOOT_FORMAT_SINGLE, },
+	{ .compatible = "u-boot,env-redundant-bool", .data = (void *)U_BOOT_FORMAT_REDUNDANT, },
+	{ .compatible = "u-boot,env-redundant-count", .data = (void *)U_BOOT_FORMAT_REDUNDANT, },
+	{ .compatible = "brcm,env", .data = (void *)U_BOOT_FORMAT_BROADCOM, },
+	{},
+};
+
+static struct platform_driver u_boot_env_driver = {
+	.probe = u_boot_env_probe,
+	.driver = {
+		.name = "u_boot_env",
+		.of_match_table = u_boot_env_of_match_table,
+	},
+};
+module_platform_driver(u_boot_env_driver);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_DESCRIPTION("U-Boot environment variables support module");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, u_boot_env_of_match_table);