Re: [PATCH RESEND] KVM: when entering real mode align segment base to 16 bytes

[Gleb Natapov <gleb@redhat.com>]

On Mon, Dec 27, 2010 at 04:55:08PM +0200, Avi Kivity wrote:
> On 12/27/2010 04:37 PM, Gleb Natapov wrote:
> >>  What's the scenario here?  And what segment is involved?  if it's fs
> >>  or gs, or maybe ss, I can see it working out, but hardly otherwise.
> >>
> >The scenario is older Seabios that lefts DS segment unaligned during
> >switch to real mode in int1587 function (copy extended memory).
> >
> 
> Did it not use %ds then?
> 
It restores %ds before first use. There can be other guests of course
that try to use %ds in protected mode. We can distinguish one from the
other.
 
> What about switching back to protected mode? I see we do restore the
> base, so it can continue to use the segment.  I guess this isn't an
> issue for 1587.
> 
Correct. 1587 does not return to protected mode again.
 
--
			Gleb.