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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.14 at 15:04, <feng.wu@xxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> And as Andrew emphasized, raising a fault in response to a failure
>> here is out of question (the only two options considering this is
>> asynchronous would be #MC or a failsafe callback, neither of which
>> really fit the purpose). Nevertheless it would be rather desirable to
>> have a way to tell the guest about the dropped write. We've got
>> a field in struct arch_vcpu_info that we could leverage for this,
>> requiring the guest to actively poll if it cares about finding out (to
>> avoid the polling this could further be combined with a new
>> per-vCPU vIRQ, or by defining another XEN_NMIREASON_* value
>> and delivering the notification via NMI).
> 
> I am not familiar with these related code actually, I try to get some
> findings in the code, but seems no good news. So maybe I have some
> basic questions here:
> 1. What is the purpose of 'struct arch_vcpu_info arch'?
> 2. Do you mean I can use the member 'unsigned long pad' of it to tell
> the guest about the dropped write.
> 3. What information about the dropped write should be sent to guest?
> 4. When guests will poll the information?
> 5. Can vIRQ be used for HVM guest? Is there an existing example in the
> current code?

With this many questions I don't think there's much point in you doing
the notification part; why don't you just start without notification,
adding of which is an enhancement only anyway?

Jan



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