From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: KVM: x86: move vapic page handling out of fast path
Date: Sun, 22 Jun 2008 08:00:11 +0300
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References: <20080619174347.GA9236@dmt.cnet>
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Cc: kvm-devel <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
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Marcelo Tosatti wrote:
> I fail to see the point of handling the vapic page grab and ref
> counting in __vcpu_run's heavyweight enter/exit path.
>
>   

It's to avoid pinning the page indefinitely.

> So move it to kvm_lapic_set_vapic_addr / kvm_free_lapic time.
>
> Other than the obvious improvement for non-Flexpriority case, this      
> kills a down_read/up_read pair in heavy exits and reduces code size.    
>   

With mmu notifiers we can do this and still not ping the page:

fast path:


if (vapic_addr && !vapic_page)
    enter_vapic();


mmu notifier:

if (gpa == vapic_addr)
    exit_vapic()


So let's wait with this until mmu notifiers are merged.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.