Re: [Xen-devel] Bisected Xen-unstable: "Segment register inaccessible for d1v0" when starting HVM guest on intel

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, July 04, 2014 3:11 PM
> To: Wu, Feng
> Cc: Andrew Cooper; Sander Eikelenboom; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: RE: Bisected Xen-unstable: "Segment register inaccessible for d1v0"
> when starting HVM guest on intel
> 
> >>> On 04.07.14 at 08:58, <feng.wu@xxxxxxxxx> wrote:
> 
> >
> >> -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: Friday, July 04, 2014 2:50 PM
> >> To: Wu, Feng
> >> Cc: Andrew Cooper; Sander Eikelenboom; xen-devel@xxxxxxxxxxxxxxxxxxxx
> >> Subject: RE: Bisected Xen-unstable: "Segment register inaccessible for
> d1v0"
> >> when starting HVM guest on intel
> >>
> >> >>> On 04.07.14 at 04:51, <feng.wu@xxxxxxxxx> wrote:
> >> > I try to reproduce this issue on my side, but I find that the per-VCPU 
> >> > guest
> >> > runstate shared memory area
> >> > is not registered by the HVM guest, so in update_runstate_area(), it
> always
> >> > returns 1 and bypass the
> >> > remaining logic. I am wondering how it is registered in your HVM guest,
> > were
> >> > you running an PVHVM guest
> >> > or HVM guest with PV drivers, I think which may register this area.
> >> >
> >> > Jan, do you have some ideas about this, Thanks a lot!
> >>
> >> You should have clarified what kind of guest(s) you tried. Pv-ops Linux,
> >> afaict, appears to register these areas not just in PV mode.
> >
> > I tried two kinds of guests:
> > 1. RHEL 6.5 with its own kernel.
> > 2. I built a 3.11.4 kernel in RHEL 6.5 and boot from this new kernel.
> >
> > Both the them don't register the 'runstate shared memory area', do I
> > need to configure something else in .config when building the kernel?
> 
> For one asking a question like this is pretty pointless without attaching
> the .config you used. And second I think you could have checked the
> code yourself: xen_hvm_setup_cpu_clockevents() calling
> xen_setup_runstate_info() gets built when CONFIG_XEN_PVHVM is
> defined.
> 

Yes, you are right, this one depends on PVH support in guest, after I configure
PVH for the guest, I can see this memory area is register by it. Thank you, Jan!

BTW, there is another question. I grep 'VCPUOP_register_vcpu_time_memory_area'
in the latest branch of Linux kernel code, but I find nothing about it. Do you 
know how
it is used by guests? Or this hypercall is being provided by Xen, but Linux 
hasn't used it yet?

Thanks,
Feng

> Jan


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