From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: GET_SUPPORTED_CPUID and irqchip (was Re: kvm_pv_unhalt and
 kernel_irqchip=off)
Date: Mon, 15 Aug 2016 20:32:37 +0200
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Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>, peterx@redhat.com,
	Andrew Jones <drjones@redhat.com>, kvm@vger.kernel.org
To: Eduardo Habkost <ehabkost@redhat.com>
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2016-08-15 15:00-0300, Eduardo Habkost:
> On Mon, Aug 15, 2016 at 07:50:59PM +0200, Radim Krčmář wrote:
> [...]
>> +static void kvm_clear_invalid_cpuid(struct kvm_vcpu *vcpu)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	struct kvm_cpuid_entry2 *best;
>> +
>> +	if (!kvm->clear_invalid_cpuid)
>> +		return;
>> +
>> +	best = kvm_find_cpuid_entry(vcpu, 1, 0);
>> +	if (best && !lapic_in_kernel(vcpu))
>> +		best->ecx &= ~F(X2APIC);
> 
> Isn't it possible to implement x2apic support in userspace APIC
> using the current KVM interfaces?

No, MSR accesses never get to userspace.  We'll probably implement it in
the future as there already has been a proposal for unhandled MSRs.