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Re: [Xen-devel] [PATCH] mm: fix LLVM code-generation issue

Hi Jan,

On 11/22/18 1:36 PM, Jan Beulich wrote:
On 22.11.18 at 14:31, <andrew.cooper3@xxxxxxxxxx> wrote:
I think Julien's point is that without explicitly barriers, CPU0's
update to system_state may not be visible on CPU1, even though the
mappings have been shot down.

Therefore, from the processors point of view, it did everything
correctly, and hit a real pagefault.

Boot time updates of system_state should be of no interest here,
as at that time the APs are all idling.

That's probably true today. But this code looks rather fragile as you don't know how this is going to be used in the future.

If you decide to gate init code with system_state, then you need a barrier to ensure the code is future proof.


Julien Grall

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