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Date: Sun, 10 Jan 2010 16:49:51 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Ian Campbell <ijc@hellion.org.uk>, Brian Gerst <brgerst@gmail.com>,
       Christian Kujau <lists@nerdbynature.de>,
       "H. Peter Anvin" <hpa@zytor.com>, Jeremy Fitzhardinge <jeremy@goop.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user page
	tables
Message-ID: <20100110134951.GD5189@lenovo>
References: <alpine.DEB.2.01.1001060240010.3483@bogon.housecafe.de> <20100106112133.GA5815@lenovo> <alpine.DEB.2.01.1001060434330.3483@bogon.housecafe.de> <4B4633D3.2070903@zytor.com> <alpine.DEB.2.01.1001071123220.3483@bogon.housecafe.de> <20100108215039.GD4967@lenovo> <73c1f2161001091750y67a852dfk7539021dcc82fa1f@mail.gmail.com> <20100110080940.GB5189@lenovo> <1263128343.2393.45.camel@cthulhu.hellion.org.uk> <20100110133628.GC5189@lenovo>
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On Sun, Jan 10, 2010 at 04:36:28PM +0300, Cyrill Gorcunov wrote:
...
> > 
> > With just the CS RPL fix below I see a GPF at kernel_thread_helper with
> > SS=3 (hence my hypothesis about NULL selectors and non-zero RPL above).
> > With both the SS and CS fixes things work fine.
> 
> any of CS,SS loaded with NULL descriptor should lead to #GP
> 

though SS with RPL=0 is allowed to be NULL descriptor in 64bit mode

> > 
> > Ian.
> > 
> > --- 
> > Subject: xen: 64 bit kernel RPL should be 0.
> > 
> ...
> 
> Good catch Ian! I've noted that Xen use it's own get_kernel_rpl
> while discussing this problem in a chat. But I must admit *I simply don't know*
> what Xen does, or how it works internally (neither I have will to learn it at
> moment :)
> 
> That said -- I'm happy if yor patch fixes problem (and it looks that
> get_kernel_rpl is guilty here indeed).
> 
> 	-- Cyrill

	-- Cyrill
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