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 13:52:40 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	Gleb Natapov <gleb@...nel.org>, Tang Chen <tangchen@...fujitsu.com>
CC:	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 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 page.
>>>> +	 */
>>>> +	struct page *page = 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 why not drop it entirely?
>>>
>>
>> I should also update kvm->arch.apic_access_page here. It is used in other
>> 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_ADDR phys address.
> If APIC_ACCESS_ADDR changes during nested guest run, non nested vmcs will still have old
> physical address. One way to fix that is to set KVM_REQ_APIC_PAGE_RELOAD 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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