From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v6 24/29] xen/x86: allow HVM guests to use
 hypercalls to bring up vCPUs
Date: Tue, 29 Sep 2015 11:37:15 +0100
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To: Jan Beulich <JBeulich@suse.com>, roger.pau@citrix.com
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, xen-devel@lists.xenproject.org, Stefano Stabellini <stefano.stabellini@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Tim Deegan <tim@xen.org>
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On 29/09/15 11:33, Jan Beulich wrote:
>>>> On 29.09.15 at 12:25, <andrew.cooper3@citrix.com> wrote:
>> On 29/09/15 11:07, Jan Beulich wrote:
>>>>>> On 29.09.15 at 12:00, <andrew.cooper3@citrix.com> wrote:
>>>> Therefore, we are back to the question of whether to provide all segment
>>>> registers, or specify a flat layout without specific selector values.  I
>>>> would prefer the former to the latter.
>>> If we don't go the CS+SS only route, then yes, I'd too prefer
>>> completing the set (I would probably agree with not adding FS
>>> and GS, and even recommend against it in the 64-bit variant,
>>> but I do insist on ES in that case).
>> I would still err on the CS/SS/DS/ES side given a straight choice.  It
>> offers more flexibility for rarer usecases.
> Okay, all four of them then for 32-bit, and just CS and SS for 64-bit?

Is SS needed for 64bit?  It is expected to be NUL just like DS and ES.

~Andrew