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Date: Wed, 03 Jun 2015 10:30:54 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PULL 2/5] apic: map APIC's MMIO region at each
 CPU's address space
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To: Igor Mammedov <imammedo@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Eduardo Habkost <ehabkost@redhat.com>, qemu-devel@nongnu.org, Chen Fan <chen.fan.fnst@cn.fujitsu.com>, =?windows-1252?Q?Andreas_F=E4?= =?windows-1252?Q?rber?= <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>



On 03/06/2015 10:29, Igor Mammedov wrote:
>>> > > +    root = address_space_root_memory_region(cpu->as);
>> > 
>> > I think just using cpu->as->root is okay.
>> > 
>>> > > +    memory_region_add_subregion_overlap(root,
>>> > > +                                        s->apicbase & MSR_IA32_APICBASE_BASE,
>>> > > +                                        &s->io_memory,
>>> > > +                                        0x1000);
>> > 
>> > I think this patch is incorrect, because you do not install a separate
>> > address space for each CPU.  Also, the CPU address space is only used
>> > with TCG so it should be guarded by "if (tcg_enabled())".
> Don't we need it be mapped on for KVM for MSI to work
> when using kvm-apic?
> 
> kvm_apic_io_ops->write =  kvm_apic_mem_write->kvm_irqchip_send_msi()

Yes, and the reason this patch worked is simply that by default cpu->as
is &address_space_memory.  The patch was just registering the same
region once per VCPU instead of 1, in the same place as before.

Paolo