Re: [Xen-devel] [PATCH v10 05/11] x86/entry: Organise the use of MSR_SPEC_CTRL at each entry/exit point

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.01.18 at 15:12, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 25/01/18 13:08, Jan Beulich wrote:
>> It may also be worthwhile again to pull up the zeroing of %edx,
>> using %dl instead of $0 in the movb (and maybe then also
>> similarly in DO_SPEC_CTRL_EXIT_TO_XEN, but there I'm less
>> certain it couldn't have a negative effect).
> 
> What negative effects are you worried about?  These macros are self
> contained.

The result of the xor then is an input to the cmp, which may be
one cycle more latency than with the immediate zero.

Jan


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