Re: [Qemu-devel] kvm: "warning: host doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21]"

[Lan Tianyu]

2016-02-25 16:39 GMT+08:00 Jan Kiszka <address@hidden>:
> On 2016-02-25 09:33, Lan Tianyu wrote:
>> 2016-02-20 17:00 GMT+08:00 Paolo Bonzini <address@hidden>:
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Jan Kiszka" <address@hidden>
>>>> To: "Eduardo Habkost" <address@hidden>, "Paolo Bonzini" <address@hidden>
>>>> Cc: "qemu-devel" <address@hidden>, "kvm" <address@hidden>
>>>> Sent: Saturday, February 20, 2016 9:09:32 AM
>>>> Subject: kvm: "warning: host doesn't support requested feature: 
>>>> CPUID.01H:ECX.x2apic [bit 21]"
>>>>
>>>> Hi all,
>>>>
>>>> I suppose 5120901a37 introduced this: qemu with kernel_irqchip=off now
>>>> generates these warnings, one per VCPU, during QEMU startup. Is the plan
>>>> to live with them until we finally have x2APIC emulation in userspace
>>>> (ie. also MSR vmexiting to there), or should we otherwise avoid it?
>>>
>>> I think it's a bug, x2apic should be auto-suppressed with 
>>> kernel_irqchip=off.
>>>
>>
>> The patch is to fix the issue.
>> ------------------------------------->8----------------------------
>> From 58f2a3a94c8e7bf9f3474bcafb6c59cc4f8bcbd9 Mon Sep 17 00:00:00 2001
>> From: Lan Tianyu <address@hidden>
>> Date: Sun, 15 Jul 2001 01:40:17 -0400
>> Subject: [PATCH] Qemu/KVM: Remove x2apic feature from CPU model when
>>  kernel_irqchip=off
>>
>> x2apic feature is in the kvm_default_props and automatically added to all
>> CPU models when KVM is enabled regardless of kernel_irqchip=off. This will
>> trigger "warning: host doesn't support requested feature: CPUID.01H:
>> ECX.x2apic [bit 21]" when kernel_irqchip=off. This patch is to remove x2apic
>> feature when kernel_irqchip=off.
>
> We know this, but it's probably worth to mention the underlying reason
> here: userspace devices don't support x2APIC.
>
>>
>> Signed-off-by: Lan Tianyu <address@hidden>
>> ---
>>  target-i386/cpu.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>> index 0d447b5..2ec7eb7 100644
>> --- a/target-i386/cpu.c
>> +++ b/target-i386/cpu.c
>> @@ -2105,6 +2105,9 @@ static void x86_cpu_load_def(X86CPU *cpu,
>> X86CPUDefinition *def, Error **errp)
>>
>>      /* Special cases not set in the X86CPUDefinition structs: */
>>      if (kvm_enabled()) {
>> +           if (!kvm_irqchip_in_kernel())
>> +               x86_cpu_change_kvm_default("x2apic", "off");
>> +
>>          x86_cpu_apply_props(cpu, kvm_default_props);
>>      }
>>
>> --
>> 1.9.3
>>
>
> Make sure to comply with the coding style (there is a checkpatch.pl also
> in QEMU). And please post as a new thread with proper subject, otherwise
> people (and tools) will not find your patch as such.
>
> Jan

Thanks for comments. Will update soon..



-- 
Best regards
Tianyu Lan