KVM: x86: Allow ARAT CPU feature

From: Jan Kiszka <[email protected]>

There is no reason to deny this feature to guests. We are emulating the APIC timer, thus are exposing it without stops in power-saving states.

---
 arch/x86/kvm/cpuid.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

index 59b69f6..6d84a9e 100644
@@ -411,6 +411,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		}
 		break;
 	}
+	case 6: /* Thermal management */
+		entry->eax = 0x4; /* allow ARAT */
+		entry->ebx = 0;
+		entry->ecx = 0;
+		entry->edx = 0;
+		break;
 	case 7: {
 		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
 		/* Mask ebx against host capability word 9 */

@@ -587,7 +593,6 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		break;
 	case 3: /* Processor serial number */
 	case 5: /* MONITOR/MWAIT */
-	case 6: /* Thermal management */
 	case 0xC0000002:
 	case 0xC0000003:
 	case 0xC0000004:

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Thanks, looks good.

Paolo
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What's the motivation of exposing ARAT to guests?

Thanks
-Yong

First of all, another step towards feature correctness for real CPU models. But I also have a setup where Linux only has APICs as clockevents (Jailhouse non-root cells), thus has no broadcast source. In that case it depends on ARAT to switch to highres mode.

Jan