[PATCH v2 06/27] x86/cpuid: Parse CPUID(0x80000000)

Add CPUID parser logic for CPUID(0x80000000).

Similar to kernel/head_32.S and kernel/cpu/common.c, verify the
CPUID(0x80000000) query output beforehand.  This is due to x86-32
machines without an extended CPUID range, where a CPUID(0x80000000) query
will just repeat the max-valid standard CPUID leaf output.

References: 8a50e5135af0 ("x86-32: Use symbolic constants, safer CPUID when enabling EFER.NX")
References: 67ad24e6d39c ("- pre5:    - Rasmus Andersen: add proper...")  # Historical git
Suggested-by: Andrew Cooper <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Ahmed S. Darwish <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
 arch/x86/include/asm/cpuid/types.h |  7 ++++++-
 arch/x86/kernel/cpu/cpuid_parser.c | 22 +++++++++++++++++++++-
 arch/x86/kernel/cpu/cpuid_parser.h |  1 +
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpuid/types.h b/arch/x86/include/asm/cpuid/types.h
index 320f152675af..d0f0e6a8a457 100644
--- a/arch/x86/include/asm/cpuid/types.h
+++ b/arch/x86/include/asm/cpuid/types.h
@@ -33,7 +33,11 @@ enum cpuid_regs_idx {
 #define CPUID_LEAF_TILE		0x1d
 
 #define CPUID_BASE_START	0x0
-#define CPUID_BASE_END		(CPUID_BASE_START + 0xffff)
+#define CPUID_EXT_START		0x80000000
+
+#define __CPUID_RANGE_END(idx)	((idx) + 0xffff)
+#define CPUID_BASE_END		__CPUID_RANGE_END(CPUID_BASE_START)
+#define CPUID_EXT_END		__CPUID_RANGE_END(CPUID_EXT_START)
 
 /*
  * Types for CPUID(0x2) parsing:
@@ -211,6 +215,7 @@ struct cpuid_leaves {
 	/*         leaf		subleaf		count */
 	CPUID_LEAF(0x0,		0,		1);
 	CPUID_LEAF(0x1,		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 949a731e03b1..731aab2ff9c0 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.c
+++ b/arch/x86/kernel/cpu/cpuid_parser.c
@@ -22,10 +22,29 @@ 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_0x80000000(const struct cpuid_parse_entry *e, struct cpuid_read_output *output)
+{
+	struct leaf_0x80000000_0 *el0 = (struct leaf_0x80000000_0 *)output->regs;
+
+	cpuid_read_subleaf(e->leaf, e->subleaf, el0);
+
+	/*
+	 * Protect against 32-bit CPUs lacking extended CPUID support: Max
+	 * extended CPUID leaf must be in the 0x80000001-0x8000ffff range.
+	 */
+	if ((el0->max_ext_leaf & 0xffff0000) != 0x80000000) {
+		*el0 = (struct leaf_0x80000000_0){ };
+		return;
+	}
+
+	output->info->nr_entries = 1;
+}
+
 static unsigned int cpuid_range_max_leaf(const struct cpuid_leaves *l, unsigned int range)
 {
 	switch (range) {
 	case CPUID_BASE_START:	return __cpuid_leaves_subleaf_0(l, 0x0).max_std_leaf;
+	case CPUID_EXT_START:   return __cpuid_leaves_subleaf_0(l, 0x80000000).max_ext_leaf;
 	default:		return 0;
 	}
 }
@@ -41,7 +60,8 @@ cpuid_range_valid(const struct cpuid_leaves *l, unsigned int leaf, unsigned int
 
 static bool cpuid_leaf_valid(const struct cpuid_leaves *l, unsigned int leaf)
 {
-	return cpuid_range_valid(l, leaf, CPUID_BASE_START, CPUID_BASE_END);
+	return	cpuid_range_valid(l, leaf, CPUID_BASE_START, CPUID_BASE_END) ||
+		cpuid_range_valid(l, leaf, CPUID_EXT_START, CPUID_EXT_END);
 }
 
 static const struct cpuid_parse_entry cpuid_common_parse_entries[] = {
diff --git a/arch/x86/kernel/cpu/cpuid_parser.h b/arch/x86/kernel/cpu/cpuid_parser.h
index b09c39a9a0b8..f440948fc2fc 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.h
+++ b/arch/x86/kernel/cpu/cpuid_parser.h
@@ -96,5 +96,6 @@ struct cpuid_parse_entry {
 	/*		  Leaf		Subleaf		Reader function */		\
 	CPUID_PARSE_ENTRY(0x0,		0,		generic),			\
 	CPUID_PARSE_ENTRY(0x1,		0,		generic),			\
+	CPUID_PARSE_ENTRY(0x80000000,	0,		0x80000000),
 
 #endif /* _ARCH_X86_CPUID_PARSER_H */
-- 
2.49.0