Add CPUID(0x2) support to the CPUID parser.

Query CPUID(0x2) only for Intel, Centaur, and Zhaoxin.  Such vendor
information was extracted from the kernel's boot code, given that

    kernel/cpu/cacheinfo.c :: init_intel_cacheinfo()

is called by

    kernel/cpu/intel.c		cpu_dev.c_x86_vendor = X86_VENDOR_INTEL
    kernel/cpu/centaur.c	cpu_dev.c_x86_vendor = X86_VENDOR_CENTAUR
    kernel/cpu/zhaoxin.c	cpu_dev.c_x86_vendor = X86_VENDOR_ZHAOXIN

At the CPUID leaf output table, keep CPUID(0x2) marked as invalidif the
whole leaf, or all of its output registers separately, were malformed.

Note, the cpuid_leaf_0x2() logic at <asm/cpuid/api.h> will be removed
once all CPUID(0x2) call sites are transformed to the new CPUID model.

References: fe78079ec07f ("x86/cpu: Introduce and use CPUID leaf 0x2 parsing helpers")
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
---
 arch/x86/include/asm/cpuid/types.h |  1 +
 arch/x86/kernel/cpu/cpuid_parser.c | 35 ++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/cpuid_parser.h |  2 ++
 3 files changed, 38 insertions(+)

diff --git a/arch/x86/include/asm/cpuid/types.h b/arch/x86/include/asm/cpuid/types.h
index d0f0e6a8a457..7bbf0671cb95 100644
--- a/arch/x86/include/asm/cpuid/types.h
+++ b/arch/x86/include/asm/cpuid/types.h
@@ -215,6 +215,7 @@ struct cpuid_leaves {
 	/*         leaf		subleaf		count */
 	CPUID_LEAF(0x0,		0,		1);
 	CPUID_LEAF(0x1,		0,		1);
+	CPUID_LEAF(0x2,		0,		1);
 	CPUID_LEAF(0x80000000,	0,		1);
 };
 
diff --git a/arch/x86/kernel/cpu/cpuid_parser.c b/arch/x86/kernel/cpu/cpuid_parser.c
index 3942ea2526f2..f3dffdd43779 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.c
+++ b/arch/x86/kernel/cpu/cpuid_parser.c
@@ -31,6 +31,41 @@ static void cpuid_read_generic(const struct cpuid_parse_entry *e, struct cpuid_r
 		cpuid_read_subleaf(e->leaf, e->subleaf + i, output->regs);
 }
 
+static void cpuid_read_0x2(const struct cpuid_parse_entry *e, struct cpuid_read_output *output)
+{
+	union leaf_0x2_regs *regs = (union leaf_0x2_regs *)output->regs;
+	struct leaf_0x2_0 *l = (struct leaf_0x2_0 *)output->regs;
+	int invalid_regs = 0;
+
+	/*
+	 * All Intel CPUs must report an iteration count of 1.  For broken hardware,
+	 * keep the leaf marked as invalid at the CPUID table.
+	 */
+	cpuid_read_subleaf(e->leaf, e->subleaf, l);
+	if (l->iteration_count != 0x01)
+		return;
+
+	/*
+	 * The most significant bit (MSB) of each CPUID(0x2) register must be clear.
+	 * If a register is malformed, replace its 1-byte descriptors with NULL.
+	 */
+	for (int i = 0; i < 4; i++) {
+		if (regs->reg[i].invalid) {
+			regs->regv[i] = 0;
+			invalid_regs++;
+		}
+	}
+
+	/*
+	 * If all of the CPUID(0x2) output registers were malformed, keep the leaf
+	 * marked as invalid at the CPUID table.
+	 */
+	if (invalid_regs == 4)
+		return;
+
+	output->info->nr_entries = 1;
+}
+
 static void cpuid_read_0x80000000(const struct cpuid_parse_entry *e, struct cpuid_read_output *output)
 {
 	struct leaf_0x80000000_0 *l = (struct leaf_0x80000000_0 *)output->regs;
diff --git a/arch/x86/kernel/cpu/cpuid_parser.h b/arch/x86/kernel/cpu/cpuid_parser.h
index 1be5c323d5eb..0e3ac9a7700d 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.h
+++ b/arch/x86/kernel/cpu/cpuid_parser.h
@@ -127,6 +127,7 @@ struct cpuid_parse_entry {
  */
 #define CPUID_COMMON_PARSE_ENTRIES							\
 	/*		  Leaf		Subleaf		Reader function */		\
+	CPUID_PARSE_ENTRY(0x2,		0,		0x2),				\
 	CPUID_PARSE_ENTRY(0x80000000,	0,		0x80000000),			\
 
 /*
@@ -160,5 +161,6 @@ struct cpuid_vendor_entry {
 
 #define CPUID_VENDOR_ENTRIES								\
  	/*		   Leaf		Vendor list */					\
+	CPUID_VENDOR_ENTRY(0x2,		X86_VENDOR_INTEL, X86_VENDOR_CENTAUR, X86_VENDOR_ZHAOXIN),\
 
 #endif /* _ARCH_X86_CPUID_PARSER_H */
-- 
2.50.1