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

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Date:	Mon, 07 Jul 2014 15:10:23 +0300
From:	Nadav Amit <nadav.amit@...il.com>
To:	Gleb Natapov <gleb@...nel.org>
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 7/7/14, 2:54 PM, Gleb Natapov wrote:
> 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?
>
If there is no general need, I will not send a fix. However, I think the 
very least a warning message should be appear if the guest relocates the 
APIC base.

Nadav

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