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, 51 insertions, 0 deletions

diff --git a/arch/x86/lib/cpu.c b/arch/x86/lib/cpu.c
new file mode 100644
index 000000000..d39fba72f
--- /dev/null
+++ b/arch/x86/lib/cpu.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/types.h>
+#include <linux/export.h>
+
+#include <asm/cpu.h>
+#include <asm/cpuid/leaf_types.h>
+
+static unsigned int __x86_family(unsigned int base_fam, unsigned int ext_fam)
+{
+	if (base_fam == 0xf)
+		base_fam += ext_fam;
+
+	return base_fam;
+}
+
+static unsigned int __x86_model(unsigned int family, unsigned int base_model,
+				unsigned int ext_model)
+{
+	if (family >= 0x6)
+		base_model |= ext_model << 4;
+
+	return base_model;
+}
+
+unsigned int x86_family(unsigned int sig)
+{
+	return __x86_family((sig >> 8) & 0xf, (sig >> 20) & 0xff);
+}
+EXPORT_SYMBOL_GPL(x86_family);
+
+unsigned int x86_model(unsigned int sig)
+{
+	return __x86_model(x86_family(sig), (sig >> 4) & 0xf, (sig >> 16) & 0xf);
+}
+EXPORT_SYMBOL_GPL(x86_model);
+
+unsigned int x86_stepping(unsigned int sig)
+{
+	return sig & 0xf;
+}
+EXPORT_SYMBOL_GPL(x86_stepping);
+
+unsigned int cpuid_family(const struct leaf_0x1_0 *l)
+{
+	return __x86_family(l->base_family_id, l->ext_family);
+}
+
+unsigned int cpuid_model(const struct leaf_0x1_0 *l)
+{
+	return __x86_model(cpuid_family(l), l->base_model, l->ext_model);
+}