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

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Date:	Fri, 18 Jul 2014 14:21:42 +0300
From:	Gleb Natapov <gleb@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.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.

On Fri, Jul 18, 2014 at 05:05:20PM +0800, Tang Chen wrote:
> Hi Gleb,
> 
> On 07/17/2014 09:57 PM, Gleb Natapov wrote:
> >On Thu, Jul 17, 2014 at 09:34:20PM +0800, Tang Chen wrote:
> >>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
> >Using patch 5/5, when apic page is migrated on L0, mmu_notifier will notify
> >L1 or L2 VMCS depending on which one happens to be running right now.
> >If it is L1 then L2's VMCS will be updated during vmentry emulation,
> 
> OK, this is easy to understand.
> 
> >if it is
> >L2 we need to request reload during vmexit emulation to make sure L1's VMCS is
> >updated.
> >
> 
> I'm a little confused here. In patch 5/5, I called make_all_cpus_request()
> to
> force all vcpus exit to host. If we are in L2, where will the vcpus exit to
> ?
> L1 or L0 ?
> 
L0. CPU always exits to L0. L1->L2 exit is emulated by nested_vmx_vmexit().

--
			Gleb.
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