linux-kernel - Re: [RFC PATCH 0/3] generic hypercall support

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Message-ID: <4A04196E.7090908@redhat.com>
Date:	Fri, 08 May 2009 14:37:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Marcelo Tosatti wrote:
>>> Also it would be interesting to see the MMIO comparison with EPT/NPT,
>>> it probably sucks much less than what you're seeing.
>>>   
>>>       
>> Why would NPT improve mmio?  If anything, it would be worse, since the  
>> processor has to do the nested walk.
>>     
>
> I suppose the hardware is much more efficient than walk_addr? There's
> all this kmalloc, spinlock, etc overhead in the fault path.
>   

mmio still has to do a walk_addr, even with npt.  We don't take the mmu 
lock during walk_addr.


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

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