linux-kernel - Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk and pte prefetch

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Date:	Sat, 03 Jul 2010 20:31:55 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk
 and pte prefetch



Avi Kivity wrote:

>>    
> 
>         if (!direct) {
>             r = kvm_read_guest_atomic(vcpu->kvm,
>                           gw->pte_gpa[level - 2],
> &curr_pte, sizeof(curr_pte));
>             if (r || curr_pte != gw->ptes[level - 2]) {
>                 kvm_mmu_put_page(shadow_page, sptep);
>                 kvm_release_pfn_clean(pfn);
>                 sptep = NULL;
>                 break;
>             }
>         }
> 
> the code you moved... under what scenario is it not sufficient?
> 

I not move those code, just use common function instead, that it's 
FNAME(check_level_mapping)(), there are do the same work.

And this check is not sufficient, since it's only checked if the
mapping is zapped or not exist, for other words only when broken this
judgment:
	is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)

but if the middle level is present and it's not the large mapping,
this check is skipped.


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