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 16:06:58 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Gleb Natapov <gleb@...nel.org>
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().

Il 11/09/2014 15:59, Gleb Natapov ha scritto:
> 
> Suppose vmcs01->APIC_ACCESS_ADDR = 0xf000. During L2 entry
> vmcs02->APIC_ACCESS_ADDR is set to 0xf000 too (by prepare_vmcs02). Now
> 0xf000 is migrated to 0x8000, mmu notifier is called, it forces vmexit,
> but vcpu is in a guest mode so vmcs02->APIC_ACCESS_ADDR is never updated
> to 0x8000 because of "if (!is_guest_mode(vcpu))" check. So what am I
> missing here?

Right, guest mode isn't left as soon as you execute nested_vmx_vmexit,
because this isn't an L2->L1 exit.  So we need an "else" for that "if
(!is_guest_mode(vcpu))", in which case the hpa is ignored and
vmcs12->apic_access_addr is used instead?

Paolo
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