linux-kernel - Re: [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC

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Date:	Fri, 1 Jul 2016 20:31:44 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	David Matlack <dmatlack@...gle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"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 10/11] KVM: x86: add KVM_CAP_X2APIC_API

2016-07-01 11:09-0700, David Matlack:
> On Thu, Jun 30, 2016 at 1:54 PM, Radim Krčmář <rkrcmar@...hat.com> wrote:
>> KVM_CAP_X2APIC_API can be enabled to extend APIC ID in get/set ioctl and MSI
>> addresses to 32 bits.  Both are needed to support x2APIC.
>>
>> The capability has to be toggleable and disabled by default, because get/set
>> ioctl shifted and truncated APIC ID to 8 bits by using a non-standard protocol
>> inspired by xAPIC and the change is not backward-compatible.
>>
>> Changes to MSI addresses follow the format used by interrupt remapping unit.
>> The upper address word, that used to be 0, contains upper 24 bits of the LAPIC
>> address in its upper 24 bits.  Lower 8 bits are reserved as 0.
>> Using the upper address word is not backward-compatible either as we didn't
>> check that userspace zeroed the word.  Reserved bits are still not explicitly
>> checked, but non-zero data will affect LAPIC addresses, which will cause a bug.
>>
>> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
>> ---
>> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
>> @@ -111,12 +111,17 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
>>  }
>>
>>  void kvm_set_msi_irq(struct kvm_kernel_irq_routing_entry *e,
>> -                    struct kvm_lapic_irq *irq)
>> +                    struct kvm_lapic_irq *irq, bool x2apic_api)
>>  {
>>         trace_kvm_msi_set_irq(e->msi.address_lo, e->msi.data);
> 
> This tracepoint should start reporting e->msi.address_hi as well now.

Good catch, thanks.