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Re: [Xen-devel] [PATCH 2/4] x86/setup: Minor cleanup to host SYSCALL MSR handling

On 13/02/17 15:30, Jan Beulich wrote:
>>>> On 13.02.17 at 16:26, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 13/02/17 15:19, Jan Beulich wrote:
>>>>>> On 13.02.17 at 15:32, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> Xen's choice of the MSR_STAR value is constant across all pcpus.  
>>>> Introduce a
>>>> new define and use it to avoid the opencoding in 
>>>> subarch_percpu_traps_init()
>>>> and restore_rest_processor_state().
>>>> Despite Intel hardware having an MSR_CSTAR register, nothing actually uses 
>>>> it
>>>> as the SYSCALL instruction raises #UD out of 64bit mode, meaning that
>>> Did you mean "32-bit"?
>> SYSCALL on Intel will #UD if CS.L == 0, so you can't even use it from a
>> compatability mode segment.
> Right - so my comment stands. Or did you mean "outside of 64-bit
> mode"?

I did, but I don't see how that is meaningfully different from what I wrote.

OTOH, It doesn't matter as I am dropping that half of the patch.


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