linux-kernel - Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for APIC ID register

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Date:	Fri, 1 Jul 2016 18:37:43 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for
 APIC ID register



On 01/07/2016 17:53, Radim Krčmář wrote:
>> >>   enable_xapic()
>> >>   id = apic_id()
>> >>   set_apic_id(id+1) // ?
>> >>   enable_x2apic()
>> >>   id == apic_id() & 0xff
>> >>   disable_apic()
>> >>   enable_xapic()
>> >>   id == apic_id()
>> >> 
> > 
> > Yes, plus checking that it "moves" appropriately between low and high bits.
> 
> x2APIC cannot use MMIO interface, so apic_id() already does the best we
> can ... if KVM is shifting wrong somwhere, then the id should differ.

Yeah, fair enough.

Paolo