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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Nov 22, 2018 at 02:03:55PM +0000, Julien Grall wrote:
> 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.

Wouldn't it be enough to declare system_state as volatile?

Roger.

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