Re: [Xen-devel] Hypercalls in Intel-VT

["Ashish Bijlani" <ashish.bijlani@xxxxxxxxx>]

thanks for your answers. really appreciate your help. however, i've some more doubts and would appreciate if you could answer the following: how does transition happen from root VMX mode to non-root VMX mode? I mean does it load Xen's CS, DS from the GDT or does it switch GDT to load Xen's GDT? Also, does it do TLB flush, provided Xen is mapped in the first 64MB of the guest  VM? thanks.

On 10/26/07, Mark Williamson <mark.williamson@xxxxxxxxxxxx> wrote:

> that means dom0 doesn't make trap to ring 0 root VMX mode for privileged
> operations like updating cr3?

Dom0 always runs paravirtualised, it can't be an HVM domain.  So it just uses
the normal paravirtualised interface, regardless of whether VMX is available
in the hardware.

Cheers,
Mark

> On 10/26/07, Dong, Eddie <eddie.dong@xxxxxxxxx> wrote:
> >  DOm0 works in ring 1 root VMX mode. Anyway can switch from ring 1 to
> > ring 0 can be used for accessing privileged resource such as INT xx, or
> > thru exception like I/O.
> >
> > But HVM works in non root VMX mode though ring=0, so you need to switch
> > from non root VMX mode to root VMX mode to access privileged resource. VM
> > Exit is the only way to do this.
> >
> >  ------------------------------
> > *From:* xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:
> > xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] *On Behalf Of *Ashish Bijlani
> > *Sent:* 2007年10月26日 9:14
> > *To:* xen-devel@xxxxxxxxxxxxxxxxxxx
> > *Subject:* Re: [Xen-devel] Hypercalls in Intel-VT
> >
> > how does dom0 on intel-vt gets privileges to access the hardware devices?
> > i mean does it get these privileges through superpages?
> >
> > On 10/25/07, Cui, Dexuan <dexuan.cui@xxxxxxxxx> wrote:
> > > > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > > > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx ]
> > >
> > > On Behalf Of Ashish Bijlani
> > >
> > > > Sent: 2007年10月26日 8:20
> > > > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > Subject: Re: [Xen-devel] Hypercalls in Intel-VT
> > > >
> > > >
> > > > could there be a way to make a transition into xen without a vmexit
> > >
> > > upon executing an iret inside a guest os krnl?
> > > I think we are talking about VMX guest -- the answer it NO...  For an
> > > VMX guest to return to Xen, a VMexit is a must. You can refert to Intel
> > > Software Developer Manual 3B for details.
> > >
> > > -- Dexuan



--
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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