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

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Date:	Thu, 17 Jul 2014 21:34:20 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Gleb Natapov <gleb@...antech.com>
CC:	Jan Kiszka <jan.kiszka@....de>, <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.

Hi Gleb,

On 07/15/2014 08:40 PM, Gleb Natapov wrote:
......
>>
>> 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.
>

Sorry, I think I don't quite understand the procedure you are talking 
about here.

Referring to the code, I think we have three machines: L0(host), L1 and L2.
And we have two types of vmexit: L2->L1 and L2->L0.  Right ?

We are now talking about this case: L2 and L1 shares the apic page.

Using patch 5/5, when apic page is migrated on L0, mmu_notifier will 
notify L1,
and update L1's VMCS. At this time, we are in L0, not L2. Why cannot we 
update
the L2's VMCS at the same time ?  Is it because we don't know how many 
L2 vms
there are in L1 ?

And, when will L2->L1 vmexit happen ?  When we enforce L1 to exit to L0 by
calling make_all_cpus_request(), is L2->L1 vmexit triggered automatically ?

Thanks.
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