From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Igor Mammedov <imammedo@redhat.com>
Subject: Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff
Date: Wed, 7 Dec 2016 16:47:16 +0100 [thread overview]
Message-ID: <20161207154715.GB15611@potion> (raw)
In-Reply-To: <8ea7ddb3-84dd-e205-a728-cc0912462362@redhat.com>
2016-12-07 13:03+0100, Paolo Bonzini:
> On 02/12/2016 20:44, Radim Krčmář wrote:
>> LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of
>> VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI,
>> but there is no way to uniquely address it using xAPIC.
>>
>> From many possible options, we chose the one that also works on real
>> hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in
>> xAPIC mode.
>>
>> KVM intentionally differs from real hardware, because real hardware
>> (Knights Landing) does just "x2apic_id & 0xff" to decide whether to
>> accept the interrupt in xAPIC mode and it can deliver one interrupt to
>> more than one physical destination, e.g. 0x123 to 0x123 and 0x23.
>>
>> Add a capability to let userspace know that we do something now.
>
> I wouldn't even bother with the capability. It's a bit borderline for
> stable, but I think it's okay. We can always Cc and let the maintainer
> reject it.
Ok, David also mentioned that I should tone down compatibility ...
Thanks to both, I'll prepare v2.
prev parent reply other threads:[~2016-12-07 15:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-02 19:43 [PATCH 0/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff Radim Krčmář
2016-12-02 19:43 ` [PATCH 1/4] KVM: x86: use delivery to self in hyperv synic Radim Krčmář
2016-12-05 14:41 ` David Hildenbrand
2016-12-05 16:03 ` Radim Krčmář
2016-12-02 19:43 ` [PATCH 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic_id Radim Krčmář
2016-12-02 19:44 ` [PATCH 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same Radim Krčmář
2016-12-02 19:44 ` [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff Radim Krčmář
2016-12-05 14:37 ` David Hildenbrand
2016-12-05 16:02 ` Radim Krčmář
2016-12-05 18:00 ` David Hildenbrand
2016-12-05 20:57 ` Radim Krčmář
2016-12-06 9:37 ` David Hildenbrand
2016-12-06 12:52 ` Radim Krčmář
2016-12-07 12:03 ` Paolo Bonzini
2016-12-07 15:47 ` Radim Krčmář [this message]
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