Re: [PATCH] KVM: MMU: Segregate mmu pages created with different cr4.pge settings

From: Alexander Graf <agraf@suse.de>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	joerg.roedel@amd.com
Subject: Re: [PATCH] KVM: MMU: Segregate mmu pages created with different cr4.pge settings
Date: Wed, 07 Jan 2009 07:49:10 +0100	[thread overview]
Message-ID: <49645066.4040009@suse.de> (raw)
In-Reply-To: <20090106164311.GA4902@amt.cnet>

Marcelo Tosatti wrote:
> On Tue, Jan 06, 2009 at 04:29:59PM +0200, Avi Kivity wrote:
>   
>> Yes...
>>
>> Looks like kvm_unsync_page can be folded into mmu_need_write_protect  
>> (after which we can drop lookup_page(), which is not a good API).  But  
>> that's after we solve the current problem.
>>
>> Looks like the addition of a second role for non-pge mode confuses the  
>> mmu.  After the second page is created, mmu_need_write_protect() will  
>> return 1, but previously existing sptes can still be writable?
>>
>> Looks like we need to call rmap_write_protect() when the new page is  
>> created.
>>     
>
> I'm not sure about the details, but I suspect that multiple shadows
> confuse NPT somehow.
>
> Alexander can you give this a try:
>   

Using this patch it works. But if I read it correctly, that doesn't
actually fix anything but only treats NPT/EPT special, which it
shouldn't, should it? Maybe this actually even breaks EPT?
I remember having seen a lot of CR4 hacks in svm.c when npt is enabled.
Maybe that is related?

Alex