linux-kernel - Re: [PATCH 2/10] KVM: MMU: fix kvm_mmu_get_spte

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Message-ID: <4D744BA5.5020607@cn.fujitsu.com>
Date:	Mon, 07 Mar 2011 11:06:13 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/10] KVM: MMU: fix kvm_mmu_get_spte_hierarchy

On 03/06/2011 12:48 AM, Marcelo Tosatti wrote:
> On Fri, Mar 04, 2011 at 06:57:27PM +0800, Xiao Guangrong wrote:
>> Don not walk to the next level if spte is mapping to the large page
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
>> ---
>>  arch/x86/kvm/mmu.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index b9bf016..10e0982 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -3819,7 +3819,8 @@ int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4])
>>  	for_each_shadow_entry(vcpu, addr, iterator) {
>>  		sptes[iterator.level-1] = *iterator.sptep;
>>  		nr_sptes++;
>> -		if (!is_shadow_present_pte(*iterator.sptep))
>> +		if (!is_shadow_present_pte(*iterator.sptep) ||
>> +		      is_last_spte(*iterator.sptep, iterator.level))
>>  			break;
>>  	}
>>  	spin_unlock(&vcpu->kvm->mmu_lock);
> 
> shadow_walk_okay covers that case.
> 

We can get the large mapping pte in the loop:

static bool shadow_walk_okay(struct kvm_shadow_walk_iterator *iterator)
{
	if (iterator->level < PT_PAGE_TABLE_LEVEL)
		return false;

	if (iterator->level == PT_PAGE_TABLE_LEVEL)
		if (is_large_pte(*iterator->sptep))
			return false;

	......
}

if level > 1 and pte.pse is set, it will return true.

And, i think this judgment is useless:
	if (iterator->level == PT_PAGE_TABLE_LEVEL)
		if (is_large_pte(*iterator->sptep))
			return false;
since if level = 1, the pte bit7 is PAT.
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