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

Avi Kivity
2010-12-27T15:15:54Z

On 12/27/2010 04:58 PM, Gleb Natapov wrote:
> 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.

Okay. Please add a printk_once() if we lose some bits here, so we know
something bad happened.

In theory we should do this for the other cases too, but they have been
there long enough.