linux-kernel - Re: [PATCH v3 1/7] KVM: MMU: fix release noslot pfn

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Message-ID: <506048D1.70403@linux.vnet.ibm.com>
Date:	Mon, 24 Sep 2012 19:49:37 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] KVM: MMU: fix release noslot pfn

On 09/24/2012 07:24 PM, Gleb Natapov wrote:
> On Mon, Sep 24, 2012 at 12:59:32PM +0800, Xiao Guangrong wrote:
>> On 09/23/2012 05:13 PM, Gleb Natapov wrote:
>>> On Fri, Sep 21, 2012 at 02:57:19PM +0800, Xiao Guangrong wrote:
>>>> We can not directly call kvm_release_pfn_clean to release the pfn
>>>> since we can meet noslot pfn which is used to cache mmio info into
>>>> spte
>>>>
>>> Wouldn't it be better to move the check into kvm_release_pfn_clean()?
>>
>> I think there is no reason for us to prefer to adding this branch in
>> the common code. :)
> 
> Is the function performance critical? Is function called without the check
> on a hot path?  The function already contains much heavier kvm_is_mmio_pfn()
> check. If most/all function invocation require check before call it's
> better to move it inside.

It is not most/all functions need do this check - it is only needed on x86 mmu
page-fault/prefetch path.

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