Message-ID: <53C51608.4080109@web.de>
Date: Tue, 15 Jul 2014 13:52:40 +0200
From: Jan Kiszka <jan.kiszka@web.de>
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MIME-Version: 1.0
To: Gleb Natapov <gleb@kernel.org>, Tang Chen <tangchen@cn.fujitsu.com>
CC: mtosatti@redhat.com, nadav.amit@gmail.com, kvm@vger.kernel.org,
        laijs@cn.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com,
        guz.fnst@cn.fujitsu.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page
 in memory.
References: <1404824492-30095-1-git-send-email-tangchen@cn.fujitsu.com> <1404824492-30095-6-git-send-email-tangchen@cn.fujitsu.com> <20140712080442.GH4399@minantech.com> <53C38D55.2040307@cn.fujitsu.com> <20140714145822.GK4399@minantech.com>
In-Reply-To: <20140714145822.GK4399@minantech.com>
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On 2014-07-14 16:58, Gleb Natapov wrote:
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index ffbe557..7080eda 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -5929,6 +5929,18 @@ static void vcpu_scan_ioapic(struct kvm_vcpu =
*vcpu)
>>>>  	kvm_apic_update_tmr(vcpu, tmr);
>>>>  }
>>>>
>>>> +static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	/*
>>>> +	 * When the page is being migrated, GUP will wait till the migrate=

>>>> +	 * entry is replaced with the new pte entry pointing to the new pa=
ge.
>>>> +	 */
>>>> +	struct page *page =3D gfn_to_page_no_pin(vcpu->kvm,
>>>> +					APIC_DEFAULT_PHYS_BASE>>  PAGE_SHIFT);
>>> If you do not use kvm->arch.apic_access_page to get current address w=
hy not drop it entirely?
>>>
>>
>> I should also update kvm->arch.apic_access_page here. It is used in ot=
her
>> places
>> in kvm, so I don't think we should drop it. Will update the patch.
> What other places? The only other place I see is in nested kvm code and=
 you can call
> gfn_to_page_no_pin() there instead of using kvm->arch.apic_access_page =
directly. But
> as far as I see nested kvm code cannot handle change of APIC_ACCESS_ADD=
R phys address.
> If APIC_ACCESS_ADDR changes during nested guest run, non nested vmcs wi=
ll still have old
> physical address. One way to fix that is to set KVM_REQ_APIC_PAGE_RELOA=
D during nested exit.

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?

Jan


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