Re: [PATCH v7 012/120] x86/cpuid: Parse CPUID(0x80000000)

On Thu, May 28, 2026 at 05:37:34PM +0200, Ahmed S. Darwish wrote:
> Add CPUID parser logic for CPUID(0x80000000).
> 
> Verify the CPUID output since legacy Intel machines without an extended
> range will repeat the highest standard CPUID leaf output instead.
> 
> This verification is similar to what is done at arch/x86/kernel/head_32.S
> and arch/x86/kernel/cpu/common.c.
> 
> References: 8a50e5135af0 ("x86-32: Use symbolic constants, safer CPUID when enabling EFER.NX")
> References: 67ad24e6d39c ("- pre5:    - Rasmus Andersen: add proper...")  # Historical git
> 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 |  4 ++++
>  arch/x86/kernel/cpu/cpuid_parser.c | 21 +++++++++++++++++++++
>  arch/x86/kernel/cpu/cpuid_parser.h |  1 +
>  3 files changed, 26 insertions(+)

Before we continue with this, I wanna a bit of a cleanup to the parser:

struct cpuid_read_output was a bit too much. And also those linebreaks should
be like I did them - this is how we usually do them.

Thx.

---
From: "Borislav Petkov (AMD)" <[email protected]>
Date: Tue, 4 Aug 2026 18:53:41 -0700
Subject: [PATCH] x86/CPU: Rename struct cpuid_read_output to struct
 cpuid_output

There's no CPUID "write" operation so there's no need to have
a cpuid_read_output thing - cpuid_output is perfectly clear. And
shortens the code just fine.

Remove the funky function signature line breaks while at it.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <[email protected]>
---
 arch/x86/kernel/cpu/cpuid_parser.c | 42 ++++++++++++++----------------
 arch/x86/kernel/cpu/cpuid_parser.h | 20 +++++++-------
 2 files changed, 29 insertions(+), 33 deletions(-)

diff --git a/arch/x86/kernel/cpu/cpuid_parser.c b/arch/x86/kernel/cpu/cpuid_parser.c
index 898b0c441431..dcf8fffbfb88 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.c
+++ b/arch/x86/kernel/cpu/cpuid_parser.c
@@ -11,14 +11,14 @@
 #include "cpuid_parser.h"
 
 /* Clear a single CPUID table entry */
-static void cpuid_clear(const struct cpuid_parse_entry *e, const struct cpuid_read_output *output)
+static void cpuid_clear(const struct cpuid_parse_entry *e, const struct cpuid_output *out)
 {
-	struct cpuid_regs *regs = output->regs;
+	struct cpuid_regs *regs = out->regs;
 
 	for (int i = 0; i < e->maxcnt; i++, regs++)
 		memset(regs, 0, sizeof(*regs));
 
-	memset(output->info, 0, sizeof(*output->info));
+	memset(out->info, 0, sizeof(*out->info));
 }
 
 /*
@@ -29,12 +29,11 @@ static void cpuid_clear(const struct cpuid_parse_entry *e, const struct cpuid_re
  * Default CPUID read function
  * Satisfies the requirements stated at 'struct cpuid_parse_entry'->read().
  */
-static void
-cpuid_read_generic(const struct cpuid_parse_entry *e, const struct cpuid_read_output *output)
+static void cpuid_read_generic(const struct cpuid_parse_entry *e, const struct cpuid_output *out)
 {
-	struct cpuid_regs *regs = output->regs;
+	struct cpuid_regs *regs = out->regs;
 
-	for (int i = 0; i < e->maxcnt; i++, regs++, output->info->nr_entries++)
+	for (int i = 0; i < e->maxcnt; i++, regs++, out->info->nr_entries++)
 		cpuid_read_subleaf(e->leaf, e->subleaf + i, regs);
 }
 
@@ -60,15 +59,14 @@ static unsigned int cpuid_range_max_leaf(const struct cpuid_table *t, unsigned i
 	}
 }
 
-static void
-__cpuid_reset_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
-		    unsigned int nr_entries, unsigned int start, unsigned int end, bool fill)
+static void __cpuid_reset_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
+				unsigned int nr_entries, unsigned int start, unsigned int end, bool fill)
 {
 	const struct cpuid_parse_entry *entry = entries;
 	unsigned int range = CPUID_RANGE(start);
 
 	for (unsigned int i = 0; i < nr_entries; i++, entry++) {
-		struct cpuid_read_output output = {
+		struct cpuid_output out = {
 			.regs = cpuid_table_regs_p(t, entry->regs_offs),
 			.info = cpuid_table_info_p(t, entry->info_offs),
 		};
@@ -76,14 +74,14 @@ __cpuid_reset_table(struct cpuid_table *t, const struct cpuid_parse_entry entrie
 		if (entry->leaf < start || entry->leaf > end)
 			continue;
 
-		cpuid_clear(entry, &output);
+		cpuid_clear(entry, &out);
 
 		/*
 		 * Read the range's anchor leaf unconditionally so that the cached
 		 * maximum valid leaf value is available for the remaining entries.
 		 */
 		if (fill && (entry->leaf == range || entry->leaf <= cpuid_range_max_leaf(t, range)))
-			entry->read(entry, &output);
+			entry->read(entry, &out);
 	}
 }
 
@@ -91,22 +89,20 @@ __cpuid_reset_table(struct cpuid_table *t, const struct cpuid_parse_entry entrie
  * Zero all cached CPUID entries within [@start-@end] range.  This is needed when
  * certain operations like MSR writes induce changes to the CPU's CPUID layout.
  */
-static void
-__cpuid_zero_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
-		   unsigned int nr_entries, unsigned int start, unsigned int end)
+static void __cpuid_zero_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
+			       unsigned int nr_entries, unsigned int start, unsigned int end)
 {
 	__cpuid_reset_table(t, entries, nr_entries, start, end, false);
 }
 
-static void
-__cpuid_fill_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
-		   unsigned int nr_entries, unsigned int start, unsigned int end)
+static void __cpuid_fill_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
+			       unsigned int nr_entries, unsigned int start, unsigned int end)
 {
 	__cpuid_reset_table(t, entries, nr_entries, start, end, true);
 }
 
-static void
-cpuid_fill_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[], unsigned int nr_entries)
+static void cpuid_fill_table(struct cpuid_table *t, const struct cpuid_parse_entry entries[],
+			     unsigned int nr_entries)
 {
 	static const struct {
 		unsigned int start;
@@ -127,8 +123,8 @@ static void __cpuid_scan_cpu_full(struct cpuinfo_x86 *c)
 	cpuid_fill_table(table, cpuid_parse_entries, nr_entries);
 }
 
-static void
-__cpuid_scan_cpu_partial(struct cpuinfo_x86 *c, unsigned int start_leaf, unsigned int end_leaf)
+static void __cpuid_scan_cpu_partial(struct cpuinfo_x86 *c, unsigned int start_leaf,
+				     unsigned int end_leaf)
 {
 	unsigned int nr_entries = ARRAY_SIZE(cpuid_parse_entries);
 	struct cpuid_table *table = &c->cpuid;
diff --git a/arch/x86/kernel/cpu/cpuid_parser.h b/arch/x86/kernel/cpu/cpuid_parser.h
index df627306cc8c..3d8337323958 100644
--- a/arch/x86/kernel/cpu/cpuid_parser.h
+++ b/arch/x86/kernel/cpu/cpuid_parser.h
@@ -35,21 +35,21 @@
  * Translation of compile time offsets to generic runtime pointers:
  */
 
-static inline struct cpuid_regs *
-cpuid_table_regs_p(const struct cpuid_table *t, unsigned long regs_offset)
+static inline struct cpuid_regs *cpuid_table_regs_p(const struct cpuid_table *t,
+						    unsigned long regs_offset)
 {
 	return (struct cpuid_regs *)((unsigned long)(&t->leaves) + regs_offset);
 }
 
-static inline struct leaf_parse_info *
-cpuid_table_info_p(const struct cpuid_table *t, unsigned long info_offset)
+static inline struct leaf_parse_info *cpuid_table_info_p(const struct cpuid_table *t,
+							 unsigned long info_offset)
 {
 	return (struct leaf_parse_info *)((unsigned long)(&t->leaves) + info_offset);
 }
 
 /**
- * struct cpuid_read_output - Output of a CPUID read operation
- * @regs:	Pointer to an array of CPUID outputs, where each array element covers the
+ * struct cpuid_output - Output of a CPUID operation
+ * @regs:	Pointer to an array of CPUID results, where each array element covers the
  *		full EAX->EDX output range.
  * @info:	Pointer to query info; for saving the number of filled elements at @regs.
  *
@@ -59,7 +59,7 @@ cpuid_table_info_p(const struct cpuid_table *t, unsigned long info_offset)
  *
  * See struct cpuid_parse_entry.read().
  */
-struct cpuid_read_output {
+struct cpuid_output {
 	struct cpuid_regs	*regs;
 	struct leaf_parse_info	*info;
 };
@@ -74,8 +74,8 @@ struct cpuid_read_output {
  *		passed to cpuid_table_info_p().
  * @maxcnt:	Maximum number of output storage entries available for the CPUID query.
  * @read:	Read function for this entry.  It must save the parsed CPUID output to the passed
- *		'struct cpuid_read_output'->regs array of size >= @maxcnt.  It must set
- *		'struct cpuid_read_output'->info.nr_entries to the number of CPUID output entries
+ *		'struct cpuid_output'->regs array of size >= @maxcnt.  It must set
+ *		'struct cpuid_output'->info.nr_entries to the number of CPUID output entries
  *		parsed and filled.  A generic implementation is provided at cpuid_read_generic().
  */
 struct cpuid_parse_entry {
@@ -84,7 +84,7 @@ struct cpuid_parse_entry {
 	unsigned int	regs_offs;
 	unsigned int	info_offs;
 	unsigned int	maxcnt;
-	void		(*read)(const struct cpuid_parse_entry *e, const struct cpuid_read_output *o);
+	void		(*read)(const struct cpuid_parse_entry *e, const struct cpuid_output *o);
 };
 
 #define __CPUID_PARSE_ENTRY(_leaf, _subleaf, _suffix, _reader_fn)		\
-- 
2.53.0

-- 
Regards/Gruss,
    Boris.

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