linux-kernel - Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page in memory.

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Date:	Tue, 15 Jul 2014 15:10:15 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	Gleb Natapov <gleb@...antech.com>,
	Tang Chen <tangchen@...fujitsu.com>
CC:	mtosatti@...hat.com, nadav.amit@...il.com, kvm@...r.kernel.org,
	laijs@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	guz.fnst@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page
 in memory.

On 2014-07-15 14:40, Gleb Natapov wrote:
>>
>> ......
>> 7922                         if (!vmx->nested.apic_access_page)
>> 7923                                 exec_control &=
>> 7924 ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
>> 7925                         else
>> 7926                                 vmcs_write64(APIC_ACCESS_ADDR,
>> 7927 page_to_phys(vmx->nested.apic_access_page));
>> 7928                 } else if
>> (vm_need_virtualize_apic_accesses(vmx->vcpu.kvm)) {
>> 7929                         exec_control |=
>> 7930 SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
>> 7931                         vmcs_write64(APIC_ACCESS_ADDR,
>> 7932 page_to_phys(vcpu->kvm->arch.apic_access_page));
>> 7933                 }
>>
>> And yes, we have the problem you said here. We can migrate the page while L2
>> vm is running.
>> So I think we should enforce L2 vm to exit to L1. Right ?
>>
> We can request APIC_ACCESS_ADDR reload during L2->L1 vmexit emulation, so
> if APIC_ACCESS_ADDR changes while L2 is running it will be reloaded for L1 too.

How should this host-managed VMCS field possibly change while L2 is running?

Jan



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