RE: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

[David Laight]

From: Andy Lutomirski
> Sent: 16 December 2019 18:06
..
> This whole discussion is about the fact that PeterZ is sceptical that
> actual x86 CPUs have as strong a memory model as the SDM suggests, and
> I'm trying to understand the exact concern.  This may or may not be
> directly relevant to the kernel. :)

The x86 memory model is pretty strong.
It has to be to support historic code - including self modifying code.
I think DOS from 1982 should still boot.

Even for SMP they probably can't relax anything from the original implementations.
(Except cpu specific kernel bits - since that has all changed since some dual 486 boxes.)

Actually the weakest x86 memory model was that defined in some P-pro
era Intel docs that said that IOR/IOW weren't sequenced with memory accesses.
Fortunately no cpu ever did that reordering, and now it isn't allowed.

	David

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