linux-kernel - [PATCH v2 15/17] x86/cpu/intel: Bound the non-architectural constant

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Message-ID: <20250211194407.2577252-16-sohil.mehta@intel.com>
Date: Tue, 11 Feb 2025 19:44:05 +0000
From: Sohil Mehta <sohil.mehta@...el.com>
To: x86@...nel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Tony Luck <tony.luck@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	"H . Peter Anvin" <hpa@...or.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Zhang Rui <rui.zhang@...el.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Laight <david.laight.linux@...il.com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org,
	linux-pm@...r.kernel.org,
	linux-hwmon@...r.kernel.org
Subject: [PATCH v2 15/17] x86/cpu/intel: Bound the non-architectural constant_tsc model checks

Constant TSC has been architectural on Intel CPUs for a while. Supported
CPUs use the architectural Invariant TSC bit in CPUID.80000007. A
Family-model check is not required for these CPUs.

Prevent unnecessary confusion but restricting the model specific checks
to CPUs that need it and moving it closer to the architectural check.

Invariant TSC was likely introduced around the Nehalam timeframe on the
Xeon side and Saltwell timeframe on the Atom side.  Due to interspersed
model numbers extend the non-architectural capability setting until
Ivybridge to be safe.

Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>

---

v2: No change.

---
 arch/x86/kernel/cpu/intel.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1b01ef4dfda2..ab195dcea50b 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -210,10 +210,6 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 {
 	u64 misc_enable;
 
-	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
-		(c->x86 == 0x6 && c->x86_model >= 0x0e))
-		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
-
 	if (c->x86 >= 6 && !cpu_has(c, X86_FEATURE_IA64))
 		c->microcode = intel_get_microcode_revision();
 
@@ -272,6 +268,11 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
 	}
 
+	/* Some older CPUs have invariant TSC but may not report it architecturally via 8000_0007 */
+	if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE) ||
+	    (c->x86_vfm >= INTEL_CORE_YONAH && c->x86_vfm <= INTEL_IVYBRIDGE))
+		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
+
 	/* Penwell and Cloverview have the TSC which doesn't sleep on S3 */
 	switch (c->x86_vfm) {
 	case INTEL_ATOM_SALTWELL_MID:
-- 
2.43.0