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Re: x86_64 and CX8

On Tue, Apr 14, 2020 at 06:34:54PM +0200, Manuel Bouyer wrote:
> hello,
> is someone aware of a x86_64 CPU which does *not* support cmpxchg8b ?
> The instruction seems mandatory since i686-class CPUs, and it seems that
> since windows XP cmpxchg8b is not optional.
> in amd64/amd64/spl.S we have 2 implementations of spllower(), which seems
> overkill if all x86-64 CPUs supports cmpxchg8b ...
> The reason I'm asking is I want to switch XENPV to cmpxchg8b versions
> of spllower and mutex_exit, and we can't use x86_patch() here.

I can test on 

cpu0: highest basic info 00000001
cpu0: highest extended info 80000018
cpu0: "AMD Opteron(tm) Processor 152"
cpu0: AMD Athlon 64 or Athlon 64 FX or Opteron (686-class), 2613.52 MHz
cpu0: family 0xf model 0x27 stepping 0x1 (id 0x20f71)

but am not sure HOW early that one is.


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