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Message-ID: <20250730042617.5620-1-suchitkarunakaran@gmail.com>
Date: Wed, 30 Jul 2025 09:56:17 +0530
From: Suchit Karunakaran <suchitkarunakaran@...il.com>
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	hpa@...or.com,
	darwi@...utronix.de,
	sohil.mehta@...el.com,
	peterz@...radead.org,
	ravi.bangoria@....com
Cc: skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Suchit Karunakaran <suchitkarunakaran@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH v3] x86/cpu/intel: Fix the constant_tsc model check for Pentium 4s

The logic to synthesize constant_tsc for Pentium 4s (Family 15) is
wrong. Since INTEL_P4_PRESCOTT is numerically greater than
INTEL_P4_WILLAMETTE, the logic always results in false and never sets
X86_FEATURE_CONSTANT_TSC for any Pentium 4 model.
The error was introduced while replacing the x86_model check with a VFM
one. The original check was as follows:
        if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
                (c->x86 == 0x6 && c->x86_model >= 0x0e))
                set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);

Fix the logic to cover all Pentium 4 models from Prescott (model 3) to
Cedarmill (model 6) which is the last model released in Family 15.

Fixes: fadb6f569b10 ("x86/cpu/intel: Limit the non-architectural constant_tsc model checks")

Cc: <stable@...r.kernel.org> # v6.15

Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>

---

Changes since v2:
- Improve commit message

Changes since v1:
- Fix incorrect logic

 arch/x86/kernel/cpu/intel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 076eaa41b8c8..6f5bd5dbc249 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -262,7 +262,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 	if (c->x86_power & (1 << 8)) {
 		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
 		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
-	} else if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE) ||
+	} else if ((c->x86_vfm >=  INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_CEDARMILL) ||
 		   (c->x86_vfm >= INTEL_CORE_YONAH  && c->x86_vfm <= INTEL_IVYBRIDGE)) {
 		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
 	}
-- 
2.50.1


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