linux-kernel - Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

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Message-ID: <4BE00D46.6050003@redhat.com>
Date:	Tue, 04 May 2010 15:04:22 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

On 05/04/2010 03:00 PM, Roedel, Joerg wrote:
> On Tue, May 04, 2010 at 05:50:50AM -0400, Avi Kivity wrote:
>    
>> On 05/04/2010 12:45 PM, Avi Kivity wrote:
>>      
>>>
>>> Just a silly bug.  kvm_pdptr_read() can cause a guest memory read on
>>> svm, in this case with the mmu lock taken.  I'll post something to fix
>>> it.
>>>        
>> I guess this was not reported because most svm machines have npt, and
>> this requires npt=0 to trigger.  Nonpae paging disables npt, so you were
>> hit.  Interestingly, nsvm makes it more likely to appear, since npt on
>> i386+pae will need the pdptrs.
>>      
> Hmm, actually it happened on 32 bit with npt enabled. I think this
> can trigger when mmu_alloc_roots is called for an pae guest because it
> accidentially tries read the root_gfn from the guest before it figures
> out that it runs with tdp and omits the gfn read from the guest.
>    

Yes.  I had a patchset which moved the 'direct' calculation before, and 
skipped root_gfn if it was direct, but it was broken.  If you like I can 
resurrect it, but it may interfere with your work.

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

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