Re: [Qemu-devel] [PATCH] Qemu/KVM: Remove x2apic feature from CPU model when kernel_irqchip is off

[Eduardo Habkost]

On Thu, Feb 25, 2016 at 11:15:12PM +0800, Lan Tianyu wrote:
> x2apic feature is in the kvm_default_props and automatically added to all
> CPU models when KVM is enabled. But userspace devices don't support x2apic
> which can't be enabled without the in-kernel irqchip. It will trigger
> warning of "host doesn't support requested feature: CPUID.01H:ECX.x2apic
> [bit 21]" when kernel_irqchip is off. This patch is to fix it via removing
> x2apic feature when kernel_irqchip is off.
> 
> Signed-off-by: Lan Tianyu <address@hidden>
> ---
>  target-i386/cpu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index c78f824..298fb62 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2125,6 +2125,10 @@ 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");

This should be NULL instead of "off". Otherwise, the warning will
be disabled if using "-cpu ...,+x2apic".

> +        }
> +

This function runs multiple times (once for each VCPU being
created). Should be harmless, though. Eventually we could move
the whole kvm_default_props logic outside cpu.c, to a KVM-x86
accel class or to common PC initialization code.


>          x86_cpu_apply_props(cpu, kvm_default_props);
>      }
>  
> -- 
> 1.9.3
> 

-- 
Eduardo