linux-kernel - Re: [PATCH 3/4] kvm, memory-hotplug: Update ept identity pagetable when it is migrated.

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Message-ID: <53B61316.2050208@cn.fujitsu.com>
Date:	Fri, 4 Jul 2014 10:36:06 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Gleb Natapov <gleb@...nel.org>
CC:	<mtosatti@...hat.com>, <kvm@...r.kernel.org>,
	<laijs@...fujitsu.com>, <isimatu.yasuaki@...fujitsu.com>,
	<guz.fnst@...fujitsu.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] kvm, memory-hotplug: Update ept identity pagetable
 when it is migrated.

Hi Gleb,

On 07/03/2014 12:34 AM, Gleb Natapov wrote:
> On Wed, Jul 02, 2014 at 05:00:36PM +0800, Tang Chen wrote:
>> ept identity pagetable is pinned in memory, and as a result it cannot be
>> migrated/hot-removed.
>>
>> But actually it doesn't need to be pinned in memory.
>>
>> This patch introduces a new vcpu request: KVM_REQ_MIGRATE_EPT to reset ept
>> indetity pagetable related variable. This request will be made when
>> kvm_mmu_notifier_invalidate_page() is called when the page is unmapped
>> from the qemu user space to reset kvm->arch.ept_identity_pagetable to NULL.
>> And will also be made when ept violation happens to reset
>> kvm->arch.ept_identity_pagetable to the new page.
>
> kvm->arch.ept_identity_pagetable is never used as a page address, just
> boolean null/!null to see if identity pagetable is initialized. I do
> not see why would we want to track its address at all. Changing it to bool
> and assigning true during initialization should be enough.

We already have kvm->arch.ept_identity_pagetable_done to indicate if the 
ept
identity table is initialized. If we make 
kvm->arch.ept_identity_pagetable to
bool, do you mean we have:

kvm->arch.ept_identity_pagetable: indicate if ept page is allocated,
kvm->arch.ept_identity_pagetable_done: indicate if ept page is initialized ?

I don't think we need this. Shall we remove 
kvm->arch.ept_identity_pagetable ?

Thanks.

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