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, 86 insertions, 0 deletions

diff --git a/arch/x86/boot/cpu.c b/arch/x86/boot/cpu.c
new file mode 100644
index 000000000..feb6dbd7c
--- /dev/null
+++ b/arch/x86/boot/cpu.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007-2008 rPath, Inc. - All Rights Reserved
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * arch/x86/boot/cpu.c
+ *
+ * Check for obligatory CPU features and abort if the features are not
+ * present.
+ */
+
+#include "boot.h"
+#include "cpustr.h"
+
+static char *cpu_name(int level)
+{
+	static char buf[6];
+
+	if (level == 64) {
+		return "x86-64";
+	} else {
+		if (level == 15)
+			level = 6;
+		sprintf(buf, "i%d86", level);
+		return buf;
+	}
+}
+
+static void show_cap_strs(u32 *err_flags)
+{
+	int i, j;
+	const unsigned char *msg_strs = (const unsigned char *)x86_cap_strs;
+	for (i = 0; i < NCAPINTS; i++) {
+		u32 e = err_flags[i];
+		for (j = 0; j < 32; j++) {
+			if (msg_strs[0] < i ||
+			    (msg_strs[0] == i && msg_strs[1] < j)) {
+				/* Skip to the next string */
+				msg_strs += 2;
+				while (*msg_strs++)
+					;
+			}
+			if (e & 1) {
+				if (msg_strs[0] == i &&
+				    msg_strs[1] == j &&
+				    msg_strs[2])
+					printf("%s ", msg_strs+2);
+				else
+					printf("%d:%d ", i, j);
+			}
+			e >>= 1;
+		}
+	}
+}
+
+int validate_cpu(void)
+{
+	u32 *err_flags;
+	int cpu_level, req_level;
+
+	check_cpu(&cpu_level, &req_level, &err_flags);
+
+	if (cpu_level < req_level) {
+		printf("This kernel requires an %s CPU, ",
+		       cpu_name(req_level));
+		printf("but only detected an %s CPU.\n",
+		       cpu_name(cpu_level));
+		return -1;
+	}
+
+	if (err_flags) {
+		puts("This kernel requires the following features "
+		     "not present on the CPU:\n");
+		show_cap_strs(err_flags);
+		putchar('\n');
+		return -1;
+	} else if (check_knl_erratum()) {
+		return -1;
+	} else {
+		return 0;
+	}
+}