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, 80 insertions, 0 deletions

diff --git a/drivers/soc/apple/tunable.c b/drivers/soc/apple/tunable.c
new file mode 100644
index 000000000..659323839
--- /dev/null
+++ b/drivers/soc/apple/tunable.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple Silicon hardware tunable support
+ *
+ * Each tunable is a list with each entry containing a offset into the MMIO
+ * region, a mask of bits to be cleared and a set of bits to be set. These
+ * tunables are passed along by the previous boot stages and vary from device
+ * to device such that they cannot be hardcoded in the individual drivers.
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/overflow.h>
+#include <linux/soc/apple/tunable.h>
+
+struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
+					       struct device_node *np,
+					       const char *name,
+					       struct resource *res)
+{
+	struct apple_tunable *tunable;
+	struct property *prop;
+	const __be32 *p;
+	size_t sz;
+	int i;
+
+	if (resource_size(res) < 4)
+		return ERR_PTR(-EINVAL);
+
+	prop = of_find_property(np, name, NULL);
+	if (!prop)
+		return ERR_PTR(-ENOENT);
+
+	if (prop->length % (3 * sizeof(u32)))
+		return ERR_PTR(-EINVAL);
+	sz = prop->length / (3 * sizeof(u32));
+
+	tunable = devm_kzalloc(dev, struct_size(tunable, values, sz), GFP_KERNEL);
+	if (!tunable)
+		return ERR_PTR(-ENOMEM);
+	tunable->sz = sz;
+
+	for (i = 0, p = NULL; i < tunable->sz; ++i) {
+		p = of_prop_next_u32(prop, p, &tunable->values[i].offset);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].mask);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].value);
+
+		/* Sanity checks to catch bugs in our bootloader */
+		if (tunable->values[i].offset % 4)
+			return ERR_PTR(-EINVAL);
+		if (tunable->values[i].offset > (resource_size(res) - 4))
+			return ERR_PTR(-EINVAL);
+	}
+
+	return tunable;
+}
+EXPORT_SYMBOL(devm_apple_tunable_parse);
+
+void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable)
+{
+	size_t i;
+
+	for (i = 0; i < tunable->sz; ++i) {
+		u32 val, old_val;
+
+		old_val = readl(regs + tunable->values[i].offset);
+		val = old_val & ~tunable->values[i].mask;
+		val |= tunable->values[i].value;
+		if (val != old_val)
+			writel(val, regs + tunable->values[i].offset);
+	}
+}
+EXPORT_SYMBOL(apple_tunable_apply);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_AUTHOR("Sven Peter <sven@kernel.org>");
+MODULE_DESCRIPTION("Apple Silicon hardware tunable support");