linux-kernel - Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter

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Date:	Thu, 11 Sep 2014 17:47:16 +0300
From:	Gleb Natapov <gleb@...nel.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Tang Chen <tangchen@...fujitsu.com>, mtosatti@...hat.com,
	nadav.amit@...il.com, jan.kiszka@....de, kvm@...r.kernel.org,
	laijs@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	guz.fnst@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page on
 migration in vcpu_enter_guest().

On Thu, Sep 11, 2014 at 04:37:39PM +0200, Paolo Bonzini wrote:
> Il 11/09/2014 16:31, Gleb Natapov ha scritto:
> >> > What if the page being swapped out is L1's APIC access page?  We don't
> >> > run prepare_vmcs12 in that case because it's an L2->L0->L2 entry, so we
> >> > need to "do something".
> > We will do something on L2->L1 exit. We will call kvm_reload_apic_access_page().
> > That is what patch 5 of this series is doing.
> 
> Sorry, I meant "the APIC access page prepared by L1" for L2's execution.
> 
> You wrote:
> 
> > if (!is_guest_mode() || !(vmcs12->secondary_vm_exec_control & ECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES))
> >     write(PIC_ACCESS_ADDR)
> > 
> > In other words if L2 shares L1 apic access page then reload, otherwise do nothing.
> 
> but in that case you have to redo nested_get_page, so "do nothing"
> doesn't work.
> 
Ah, 7/7 is new in this submission. Before that this page was still
pinned.  Looking at 7/7 now I do not see how it can work since it has no
code for mmu notifier to detect that it deals with such page and call
kvm_reload_apic_access_page().  I said to Tang previously that nested
kvm has a bunch of pinned page that are hard to deal with and suggested
to iron out non nested case first :(

--
			Gleb.
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