linux-kernel - Re: [PATCH 4/4] kvm, mem-hotplug: Update apic access page when it is migrated.

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Date:	Mon, 7 Jul 2014 14:54:47 +0300
From:	Gleb Natapov <gleb@...nel.org>
To:	Nadav Amit <nadav.amit@...il.com>
Cc:	Tang Chen <tangchen@...fujitsu.com>, 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 4/4] kvm, mem-hotplug: Update apic access page when it is
 migrated.

On Mon, Jul 07, 2014 at 02:42:27PM +0300, Nadav Amit wrote:
> Tang,
> 
> Running some (unrelated) tests I see that KVM does not handle APIC base
> relocation correctly. When the base is changed, kvm_lapic_set_base just
> changes lapic->base_address without taking further action (i.e., modifying
> the VMCS apic address in VMX).
> 
> This patch follows KVM bad behavior by using the constant
> VMX_APIC_ACCESS_PAGE_ADDR instead of lapic->base_address.
There is no OS out there that relocates APIC base (in fact it was not always
relocatable on real HW), so there is not point in complicating the code to support
it. In fact current APIC_ACCESS_ADDR handling relies on the fact that all vcpus
has apic mapped at the same address.

> 
> Anyhow, I didn't see anything that would make my life (in fixing the lapic
> base issue) too difficult. Yet, feel free in making it more "fix-friendly".
> 
Why would you want to fix it?

> Thanks,
> Nadav
> 
> On 7/7/14, 12:52 PM, Tang Chen wrote:
> >Hi Gleb,
> >
> >The guest hang problem has been solved.
> >
> >When mmu_notifier is called, I set VMCS APIC_ACCESS_ADDR to the new value
> >instead of setting it to 0. And only update kvm->arch.apic_access_page in
> >the next ept violation.
> >
> >The guest is running well now.
> >
> >I'll post the new patches tomorrow. ;)
> >
> >Thanks.
> >

--
			Gleb.
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