linux-kernel - Re: [PATCH v5 2/9] KVM: MMU: fix race between 'walk

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Message-ID: <4C39E5D7.7030703@redhat.com>
Date:	Sun, 11 Jul 2010 18:40:07 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 2/9] KVM: MMU: fix race between 'walk_addr' and 'fetch'

On 07/11/2010 03:52 PM, Avi Kivity wrote:
> On 07/06/2010 01:45 PM, Xiao Guangrong wrote:
>> 'walk_addr' is out of mmu_lock's protection, so while we handle 'fetch',
>> then guest's mapping has modifited by other vcpu's write path, such as
>> invlpg, pte_write and other fetch path
>>
>> Fixed by checking all level's mapping
>>
>>
>> @@ -319,22 +319,23 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, 
>> gva_t addr,
>>           direct_access&= ~ACC_WRITE_MASK;
>>
>>       for_each_shadow_entry(vcpu, addr, iterator) {
>> +        bool nonpresent = false, last_mapping = false;
>> +
>
> I don't like these two new variables, but no suggestion at the 
> moment.  I'll try to simplify this loop later.
>
> One idea may be:
>
>    while (level > walker.level) {
>          handle indirect pages
>    }
>    while (level > hlevel) {
>          handle direct pages
>    }
>    handle last spte
>
> I'm worried that this change is too big for backporting, but no 
> suggestions on how to make it smaller, so we'll have to accept it.

Okay, I couldn't resist, posting this soon.

-- 
error compiling committee.c: too many arguments to function

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