Re: [PATCH v7 012/120] x86/cpuid: Parse CPUID(0x80000000)
From: Borislav Petkov
Date: Tue Aug 04 2026 - 22:54:03 EST
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 <darwi@xxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Link: https://lore.kernel.org/r/d4fcfd91-cc92-4b3c-9dd2-56ecd754cecc@xxxxxxxxxx
> ---
> 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)" <bp@xxxxxxxxx>
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) <bp@xxxxxxxxx>
---
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.
https://people.kernel.org/tglx/notes-about-netiquette