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Message-ID: <20250506050437.10264-25-darwi@linutronix.de>
Date: Tue, 6 May 2025 07:04:35 +0200
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Andrew Cooper <andrew.cooper3@...rix.com>,
"H. Peter Anvin" <hpa@...or.com>,
John Ogness <john.ogness@...utronix.de>,
x86@...nel.org,
x86-cpuid@...ts.linux.dev,
LKML <linux-kernel@...r.kernel.org>,
"Ahmed S. Darwish" <darwi@...utronix.de>
Subject: [PATCH v1 24/26] x86/cpuid: scanner: Add CPUID table rescan support
Add system CPUID table(s) rescan support through cpuid_rescan_cpu().
This will be needed for handling events that can change the system CPUID
state; e.g. disabing the Processor Serial Number (PSN) or performing a
late microcode update.
Follow-up commits will change the call sites in need of CPUID table
rescan one by one.
Signed-off-by: Ahmed S. Darwish <darwi@...utronix.de>
---
arch/x86/include/asm/cpuid/table_api.h | 1 +
arch/x86/kernel/cpu/cpuid_scanner.c | 52 +++++++++++++++++++++++---
2 files changed, 47 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/cpuid/table_api.h b/arch/x86/include/asm/cpuid/table_api.h
index 5c4788741dfb..af145fbed9f1 100644
--- a/arch/x86/include/asm/cpuid/table_api.h
+++ b/arch/x86/include/asm/cpuid/table_api.h
@@ -115,5 +115,6 @@
(struct cpuid_regs *)cpudata_cpuid_index(_cpuinfo, _leaf, _idx)
void cpuid_scan_cpu(struct cpuinfo_x86 *c);
+void cpuid_rescan_cpu(struct cpuinfo_x86 *c);
#endif /* _ASM_X86_CPUID_TABLE_API_H */
diff --git a/arch/x86/kernel/cpu/cpuid_scanner.c b/arch/x86/kernel/cpu/cpuid_scanner.c
index 664946ebe675..74d34c06d8de 100644
--- a/arch/x86/kernel/cpu/cpuid_scanner.c
+++ b/arch/x86/kernel/cpu/cpuid_scanner.c
@@ -149,6 +149,36 @@ static void cpuid_scan(const struct cpuid_scan_info *info)
}
}
+/*
+ * @c: CPU capability structure associated with the current CPU
+ * @clear_cpuid_table: Zero out the CPUID table before populating it.
+ *
+ * The CPUID scanner code expects a zeroed table since the accessor macros at
+ * <cpuid/table_api.h> use the leaf's "nr_entries" field as a marker for its
+ * validity (otherwise NULL is returned.)
+ *
+ * At boot time, all CPUID tables within the CPU capability structure(s) are
+ * already zeroed. For subsequent CPUID table scans, which are normally done
+ * after hardware state changes, the table might contain stale data that must
+ * be cleared beforehand; e.g., a CPUID leaf that is no longer available, but
+ * with a "nr_entries" value bigger than zero.
+ */
+static void __cpuid_scan_cpu(struct cpuinfo_x86 *c, bool clear_cpuid_table)
+{
+ struct cpuid_table *table = &c->cpuid_table;
+
+ const struct cpuid_scan_info info = {
+ .cpuid_table = table,
+ .entries = cpuid_common_scan_entries,
+ .nr_entries = cpuid_common_scan_entries_size,
+ };
+
+ if (clear_cpuid_table)
+ memset(table, 0, sizeof(*table));
+
+ cpuid_scan(&info);
+}
+
/**
* cpuid_scan_cpu() - Populate CPUID data for the current CPU
* @c: CPU capability structure associated with the current CPU
@@ -159,11 +189,21 @@ static void cpuid_scan(const struct cpuid_scan_info *info)
*/
void cpuid_scan_cpu(struct cpuinfo_x86 *c)
{
- const struct cpuid_scan_info info = {
- .cpuid_table = &c->cpuid_table,
- .entries = cpuid_common_scan_entries,
- .nr_entries = cpuid_common_scan_entries_size,
- };
+ __cpuid_scan_cpu(c, false);
+}
- cpuid_scan(&info);
+/**
+ * cpuid_rescan_cpu() - Re-populate CPUID data for the current CPU
+ * @c: CPU capability structure associated with the current CPU
+ *
+ * Zero-out the CPUID table embedded within @c, then re-populate it using
+ * a fresh CPUID scan. Since all the CPUID instructions are run locally,
+ * this function must be called on the CPU associated with @c.
+ *
+ * A CPUID table rescan is usually required after system changes that can
+ * affect CPUID state; e.g., Processor Serial Number (PSN) disable.
+ */
+void cpuid_rescan_cpu(struct cpuinfo_x86 *c)
+{
+ __cpuid_scan_cpu(c, true);
}
--
2.49.0
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