Re: [Xen-devel] [PATCH] ARM: cache coherence problem in guestcopy.c

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-07-02 at 21:14 +0900, Sengul Thomas wrote:
> On Tue, Jul 2, 2013 at 6:38 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Thu, 2013-06-20 at 08:34 +0000, Jaeyong Yoo wrote:
> >> > On Tue, 2013-06-18 at 13:18 +0100, Ian Campbell wrote:
> >> > > On Tue, 2013-06-18 at 12:05 +0000, Jaeyong Yoo wrote:
> >> > > > > We were also speculating that we probably want some DMBs in
> >> > > > > context_switch_{from,to} as well as at return_to_guest.
> >> > > >
> >> > > > Actually, I just learned ReOrder Buffer, and it looks like so.
> >> >
> >> > Does this patch help with the issue you are seeing?
> >>
> >> I tried the combinations and it does not work.
> >
> > As an experiment can you try the same patch with dsb instead of dmb
> > throughout?
> 
> I tried several ways to recreate the problem I was having, but I
> failed. I was having
> that problem with some printks place to place, and sadly, I don't
> remember the printk positions.
> I'm sorry.

Oh yes, I'd forgotten that you weren't able to reproduce any more.

Oh well, I think the switch to Inner-shareable mappings in Xen is likely
to remove the issue and I think the justification for the dmb patch in
(un)map_domain_page is pretty good. So hopefully this issue will just go
away for good once we apply those (and if not we can always
reinvestigate).

> 
> Jaeyong
> 
> >
> > Could you also try the patch from my series "xen: arm: map normal memory
> > as inner shareable, reduce scope of various barriers" in
> > <1372435809.8976.169.camel@xxxxxxxxxxxxxxxxxxxxxx>, speaking with ARM
> > they reminded me that Xen currently uses Outer-shareable mappings while
> > Linux uses Inner-, which is more than likely the root cause of the issue
> > you are seeing. You probably want the dmb() patch as well to avoid
> > speculative fetches.
> >
> > Ian.
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel



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