linux-kernel - Re: [PATCH 1/4] KVM: MMU: fix permission

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Message-ID: <56FB73E0.7060601@redhat.com>
Date:	Wed, 30 Mar 2016 08:36:16 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM: MMU: fix permission_fault()



On 30/03/2016 03:56, Xiao Guangrong wrote:
>> x86/access.flat is currently using the "other" definition, i.e., PFEC.PK
>> is only set if W=1 or CR0.WP=0 && PFEC.U=0 or PFEC.W=0.  Can you use it
>> (with ept=1 of course) to check what the processor is doing?
> 
> Sure.
> 
> And ept=1 is hard to trigger MMU issue, i am enabling PKEY on shadow
> MMU, let's see what will happen. ;)

No, don't do that!

ept=1 lets you test what the processor does.  It means you cannot test
permission_fault(), but what we want here is just reverse engineering
the microcode.  ept=1 lets you do exactly that.

Paolo