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 20:28:22 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Gleb Natapov <gleb@...nel.org>
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 07/15/2014 08:09 PM, Gleb Natapov wrote:
> On Tue, Jul 15, 2014 at 01:52:40PM +0200, Jan Kiszka wrote:
......
>>
>> I cannot follow your concerns yet. Specifically, how should
>> APIC_ACCESS_ADDR (the VMCS field, right?) change while L2 is running? We
>> currently pin/unpin on L1->L2/L2->L1, respectively. Or what do you mean?
>>
> I am talking about this case:
>           if (cpu_has_secondary_exec_ctrls()) {a
>           } else {
>               exec_control |=
>                  SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
>              vmcs_write64(APIC_ACCESS_ADDR,
>                  page_to_phys(vcpu->kvm->arch.apic_access_page));
>           }
> We do not pin here.
>

Hi Gleb,


7905                 if (exec_control & 
SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES) {
......
7912                         if (vmx->nested.apic_access_page) /* 
shouldn't happen */
7913 
nested_release_page(vmx->nested.apic_access_page);
7914                         vmx->nested.apic_access_page =
7915                                 nested_get_page(vcpu, 
vmcs12->apic_access_addr);

I thought you were talking about the problem here. We pin 
vmcs12->apic_access_addr
in memory. And I think we should do the same thing to this page as to L1 
vm.
Right ?

......
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 ?

Thanks.


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