Re: [Xen-devel] [PATCH v6 24/29] xen/x86: allow HVM guests to use hypercalls to bring up vCPUs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.09.15 at 12:37, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 29/09/15 11:33, Jan Beulich wrote:
>>>>> On 29.09.15 at 12:25, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 29/09/15 11:07, Jan Beulich wrote:
>>>>>>> On 29.09.15 at 12:00, <andrew.cooper3@xxxxxxxxxx> 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.

Indeed, we should be able to get away without it. And for CS all
we'd need would be a selector.

Jan


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