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

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Message-ID: <20140707121505.GQ18167@minantech.com>
Date:	Mon, 7 Jul 2014 15:15:05 +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 03:10:23PM +0300, Nadav Amit wrote:
> 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
It is much more works that it may look like for no apparent gain.

> very least a warning message should be appear if the guest relocates the
> APIC base.
> 
Warning is fine. Make it _once().

--
			Gleb.
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