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

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Date:	Fri, 4 Jul 2014 12:49:50 +0300
From:	Gleb Natapov <gleb@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.com>
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.

On Fri, Jul 04, 2014 at 10:36:06AM +0800, Tang Chen wrote:
> 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 ?
> 
ept_identity_pagetable also means that a memory slot for identity page is initialized.

> I don't think we need this. Shall we remove kvm->arch.ept_identity_pagetable
> ?
> 
May be those two can be consolidated somehow, but lets leave it to a separate patch
to make this one simpler.

--
			Gleb.
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