Re: [Xen-devel] [hybrid]: unable to boot hvm due to eflags.ID

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-05-04 at 11:49 +0100, Tim Deegan wrote:
> At 10:08 +0100 on 04 May (1336126102), Ian Campbell wrote:
> > What does the guest EFLAGS actually contain at this point? Is it
> > different to what it contains on non-hybrid dom0?
> > 
> > How do we execute 16 bit code in a VMX guest these days, using vm86 or
> > by emulation?
> 
> Both, and also sometimes neither. :) 

Of course ;-)

> If the chip supports it, we just run in real mode inside the VM (this is
> called "unrestricted guest" in the VMX code and will be reported in the
> Xen boot messages).

Thanks, I thought this had been added but didn't know the name of the
feature.

> Otherwise we run in vm86 when we can, and emulate things that vm86
> doesn't support, and all I/O.  We also have to emulate when the segment
> state is wierd (e.g., big-real-mode) because the VMENTER into vm86 has
> stricter checks on segment state than actual real mode.
> 
> > How does that interact with EFLAGS_ID I wonder (although
> > why hybrid dom0 would have any bearing on this I've no idea).
> 
> I'm not aware of anything deliberately tinkering with EFLAGS_ID,

I couldn't find any use other than the definition, although it maybe
open coded somewhere.

> but
> it's possible that vm86 interacts with it (of that we accidentally lose
> some parts of EFLAGS in emulation).

Yeah, but I can't figure out why hybrid dom0 would change that...

Ian,


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