linux-kernel - Re: [PATCH] x86: correctly initialize the CS base on reset

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Date:	Tue, 19 Mar 2013 19:07:54 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH] x86: correctly initialize the CS base on reset

On Tue, Mar 19, 2013 at 05:41:45PM +0100, Jan Kiszka wrote:
> On 2013-03-19 16:43, Gleb Natapov wrote:
> > On Tue, Mar 19, 2013 at 04:30:26PM +0100, Paolo Bonzini wrote:
> >> The CS base was initialized to 0 on VMX (wrong, but usually overridden
> >> by userspace before starting) or 0xf0000 on SVM.  The correct value is
> >> 0xffff0000, and VMX is able to emulate it now, so use it.
> >>
> >> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > Reviewed-by: Gleb Natapov <gleb@...hat.com>
> 
> Just for the history (as I was wondering where this came from): CS base
> used to be set to 0xf0000 on VMX as well, but that was changed by
> b246dd5d to only affect guests when unrestricted mode is missing. That
> change actually left the base uninitialized.
> 
Looking at the code before b246dd5d it sets CS base to 0xf0000 only if it was
0xffff0000. This is the same as with current code: fix_rmode_seg() does
it.

--
			Gleb.
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