[PATCH v3] x86/cpu/intel: Fix the constant_tsc model check for Pentium 4s

Suchit Karunakaran
2025-07-30T04:26:28Z

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@vger.kernel.org> # v6.15

Signed-off-by: Suchit Karunakaran <suchitkarunakaran@gmail.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