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

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Message-ID: <20140911142121.GD26540@minantech.com>
Date:	Thu, 11 Sep 2014 17:21:21 +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 04:06:58PM +0200, Paolo Bonzini wrote:
> 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?
> 
As far as I can tell the if that is needed there is:

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.

--
			Gleb.
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