Hi Suchit,
The patch looks good to me except for a few nits below.
On 7/29/2025 9:26 PM, Suchit Karunakaran wrote:
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.
A blank line here would be useful to separate the two paragraphs.
The error was introduced while replacing the x86_model check with a VFM one. The original check was as follows:
Maybe to make it more precise and avoid confusion.
The original check before the erroneous code 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
Reviewed-by: Sohil Mehta sohil.mehta@intel.com (without the blank lines as Greg mentioned)
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) ||
The alignment here seems to have changed because the extra space after INTEL_P4_PRESCOTT was moved before it. The current code has alignment matched with the below line. It isn't a big deal, but keeps the code easier to read.
(c->x86_vfm >= INTEL_CORE_YONAH && c->x86_vfm <= INTEL_IVYBRIDGE)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
}