From: Sohil Mehta <[email protected]> X86_FEATURE_CONSTANT_TSC is a Linux-defined, synthesized feature flag. It is used across several vendors. Intel CPUs will set the feature when the architectural CPUID.80000007.EDX[1] bit is set. There are also some Intel CPUs that have the X86_FEATURE_CONSTANT_TSC behavior but don't enumerate it with the architectural bit. Those currently have a model range check.
Today, virtually all of the CPUs that have the CPUID bit *also* match the "model >= 0x0e" check. This is confusing. Instead of an open-ended check, pick some models (INTEL_IVYBRIDGE and P4_WILLAMETTE) as the end of goofy CPUs that should enumerate the bit but don't. These models are relatively arbitrary but conservative pick for this. This makes it obvious that later CPUs (like Family 18+) no longer need to synthesize X86_FEATURE_CONSTANT_TSC. Signed-off-by: Sohil Mehta <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Link: https://lore.kernel.org/r/[email protected] Link: https://git.kernel.org/tip/fadb6f569b10bf668677add876ed50586931b8f3 [Port to Xen] Signed-off-by: Kevin Lampis <[email protected]> Signed-off-by: Andrew Cooper <[email protected]> --- xen/arch/x86/cpu/intel.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c index 584588e406f2..18b3c79dc97f 100644 --- a/xen/arch/x86/cpu/intel.c +++ b/xen/arch/x86/cpu/intel.c @@ -637,14 +637,13 @@ static void cf_check init_intel(struct cpuinfo_x86 *c) /* Work around errata */ Intel_errata_workarounds(c); - if ((c->x86 == 0xf && c->x86_model >= 0x03) || - (c->x86 == 0x6 && c->x86_model >= 0x0e)) - __set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability); if (cpu_has(c, X86_FEATURE_ITSC)) { __set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability); __set_bit(X86_FEATURE_NONSTOP_TSC, c->x86_capability); __set_bit(X86_FEATURE_TSC_RELIABLE, c->x86_capability); - } + } else if ((c->vfm >= INTEL_P4_PRESCOTT && c->vfm <= INTEL_P4_CEDARMILL) || + (c->vfm >= INTEL_CORE_YONAH && c->vfm <= INTEL_IVYBRIDGE)) + __set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability); if ((opt_cpu_info && !(c->apicid & (c->x86_num_siblings - 1))) || c == &boot_cpu_data ) base-commit: 52e801093b6d9f72944328925588b227d7114f8e -- 2.39.5
