[PATCH] KVM: x86: Allow ARAT CPU feature

[PATCH] KVM: x86: Allow ARAT CPU feature

[Jan Kiszka]

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From: Jan Kiszka <jan.kiszka@siemens.com>

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.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 arch/x86/kvm/cpuid.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 59b69f6..6d84a9e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -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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Re: [PATCH] KVM: x86: Allow ARAT CPU feature

[Paolo Bonzini]

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On 24/05/2015 17:22, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> 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.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Thanks, looks good.

Paolo
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Re: [PATCH] KVM: x86: Allow ARAT CPU feature

[Yong Wang]

On Mon, May 25, 2015 at 03:24:05PM +0200, Paolo Bonzini wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
> 
> 
> 
> On 24/05/2015 17:22, Jan Kiszka wrote:
> > From: Jan Kiszka <jan.kiszka@siemens.com>
> > 
> > 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.
> > 
> > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> 
> Thanks, looks good.
> 

What's the motivation of exposing ARAT to guests?

Thanks
-Yong

Re: [PATCH] KVM: x86: Allow ARAT CPU feature

[Jan Kiszka]

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On 2015-05-26 03:37, Yong Wang wrote:
> On Mon, May 25, 2015 at 03:24:05PM +0200, Paolo Bonzini wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA256
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>>
>>
>> On 24/05/2015 17:22, Jan Kiszka wrote:
>>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> 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.
>>>
>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> Thanks, looks good.
>>
> 
> What's the motivation of exposing ARAT to guests?

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


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