Re: [Xen-devel] state of guest at start-up

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 4/4/07 09:46, "Max Dmitrichenko" <dmitrmax@xxxxxxxxx> wrote:

> 1) What are the status of event channels mask at the start of the day?
> My experiments showed that all the event channels are unmasked - is
> this right? In the sources of Mini-OS, I have found a comment saying
> that event channels are masked at the start. But this seems to be
> obsolete, or do I make something wrong?

The vcpu_info[cpu].evtchn_upcall_mask fields are all set to 1. This prevents
upcalls on all vcpus. The per-event-channel masks (shared_info.evtchn_mask)
is initialised to all zeroes.

> 2) What is the meaning of shared_info.vcpu_info[0].evtchn_upcall_mask?
> I thought that it masks all the event channels on the VCPU #0, but
> this seems wrong, i.e. when I set this to 0xff, the hypervisor
> callback is still being called. I have to set the
> shared_info.evtchn_mask to all ones in order to mask all the event
> channels. Is this behavour correct?

No. vcpu_info[cpu].evtchn_upcall_mask definitely stops callbacks via the
hypervisor_callback.

> 3) How to determine current VCPU number?

As you would if running natively -- probably by stack-pointer arithmetic and
have some per-cpu info stashed at the bottom of the stack page.

> 4) When I map the shared_info MFN into my OS's space via
> update_va_mapping hypercall and then take the dump of the domain with
> `xm dump-core -C ...`, the page where the shared_info supposed to be
> mapped to is filled with all zeroes. Is this normal, of that means
> that mapping was unsuccessful.

If you don't include the shared_info page in your phys-to-machine map then
dump-core will not dump the page contents.

 -- Keir


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