linux-kernel - Re: [PATCH 3/3] KVM: SVM: Clean up rip handling in vmrun emulation

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Message-ID: <20100904193241.GB8162@8bytes.org>
Date:	Sat, 4 Sep 2010 21:32:42 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Alexander Graf <agraf@...e.de>
Cc:	"Roedel, Joerg" <joerg.roedel@....com>,
	Avi Kivity <avi@...hat.com>,
	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 3/3] KVM: SVM: Clean up rip handling in vmrun emulation

On Fri, Sep 03, 2010 at 11:29:11PM +0200, Alexander Graf wrote:
> Any reason we can't use the next_rip information here? A hypervisor
> could potentially do badness and put a prefix here, thus break all the
> logic, right?

Next_rip is not available on older hardware. Yes, this problem exists in
theory (as it does with rdmsr/wrmsr, cpuid, ... too). But a fix for this
on non-next-rip capable hardware would involve the instruction emulator
and kills all performance there. So we use this stupid and fast solution
here which works for all hypervisors I tested :-)

> (yes, I know, I wrote that code, but still ...)

When you wrote that code next_rip capable hardware was not available, so
don't worry :-)


	Joerg
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