linux-kernel - Re: [PATCH 1/3] KVM: MMU: release noslot pfn on the fail path properly

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Message-ID: <504DA6D6.5030704@linux.vnet.ibm.com>
Date:	Mon, 10 Sep 2012 16:37:42 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 1/3] KVM: MMU: release noslot pfn on the fail path properly

On 09/10/2012 04:22 PM, Avi Kivity wrote:
> On 09/07/2012 09:13 AM, 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
>>
>> Introduce mmu_release_pfn_clean to do this kind of thing
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> ---
>>  arch/x86/kvm/mmu.c         |   19 ++++++++++++++-----
>>  arch/x86/kvm/paging_tmpl.h |    4 ++--
>>  2 files changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 399c177..3c10bca 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2432,6 +2432,16 @@ done:
>>  	return ret;
>>  }
>>
>> +/*
>> + * The primary user is page fault path which call it to properly
>> + * release noslot_pfn.
>> + */
>> +static void mmu_release_pfn_clean(pfn_t pfn)
>> +{
>> +	if (!is_error_pfn(pfn))
>> +		kvm_release_pfn_clean(pfn);
>> +}
>> +
> 
> Too many APIs, each slightly different.  How do I know which one to call?

It is only used in mmu and it is a static function.

> 
> Please change kvm_release_pfn_*() instead, calling some arch hook (or
> even #ifdef CONFIG_KVM_HAS_FAST_MMIO) to check for the special case.

We only need to call it on page fault path. If we change the common API
other x86 components have to suffer from it.

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