linux-kernel - Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter

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Message-ID: <54119E01.9000908@redhat.com>
Date:	Thu, 11 Sep 2014 15:05:05 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Gleb Natapov <gleb@...nel.org>
CC:	Tang Chen <tangchen@...fujitsu.com>, mtosatti@...hat.com,
	nadav.amit@...il.com, jan.kiszka@....de, kvm@...r.kernel.org,
	laijs@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	guz.fnst@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page
 on migration in vcpu_enter_guest().

Il 11/09/2014 13:30, Gleb Natapov ha scritto:
>> > +			vmcs_write64(APIC_ACCESS_ADDR, page_to_phys(page));
>> > +			/*
>> > +			 * Do not pin apic access page in memory so that memory
>> > +			 * hotplug process is able to migrate it.
>> > +			 */
>> > +			put_page(page);
>> >  		}
> This code is in prepare_vmcs02() and is executed during L1->L2 vmentry. What happens
> when apic access page is migrated while L2 is running? It needs to be update somewhere.

Before it is migrated, the MMU notifier is called and will force a
vmexit on all CPUs.  The reload code will call GUP again on the page
again and swap it in.

Paolo

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