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

From: Avi Kivity <avi@redhat.com>
To: Alexander Graf <agraf@suse.de>
Cc: Marcelo Tosatti <mtosatti@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 12:19:26 +0200	[thread overview]
Message-ID: <496481AE.1060102@redhat.com> (raw)
In-Reply-To: <49645066.4040009@suse.de>

Alexander Graf wrote:
> 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? 

The patch doesn't fix the bug but is nevertheless correct.  cr4.pge only 
matters to the mmu if using the shadow mmu; with tdp it only wastes 
memory (and exposes the bug which you encountered).

So, wrt to the bug you saw, it's a workaround, but it's also a correct 
fix for another bug.

> Maybe this actually even breaks EPT?
>   

It shouldn't.

> I remember having seen a lot of CR4 hacks in svm.c when npt is enabled.
> Maybe that is related?
>   

No.  cr4 controls the guest mmu, but with npt the guest mmu is 
completely virtualized, so we need to ignore those bits.

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