linux-kernel - Re: [PATCH 2/2] KVM: SVM: Emulate next

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Message-ID: <20100728121822.GH26098@amd.com>
Date:	Wed, 28 Jul 2010 14:18:22 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Avi Kivity <avi@...hat.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 2/2] KVM: SVM: Emulate next_rip svm feature

On Wed, Jul 28, 2010 at 07:57:36AM -0400, Avi Kivity wrote:

> If the instruction opcode is on mmio, the processor never sees the 
> opcode and thus can not intercept.  Or the processor may see one 
> instruction, which is not intercepted, but by the time the emulator 
> kicks in a different instruction takes its place, since another vcpu is 
> evilly cross-modifying the code.

Right. X-modifying code is a problem too.

> The guest (L2 in this case) is doomed since it execution cannot 
> continue.  But L1 and L0 are fine.  The problem with L2 avoiding 
> intercepts is that L2 can change control registers and take over L1.

Right too. We can not ignore it. The right fix is probably a check for
the instruction intercepts right after the decoder has run and before
the emulator ran.

	Joer

-- 
Joerg Roedel - AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

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