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Re: [Xen-devel] TLB flushing in x86's map_pages_to_xen()

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Tue, 15 May 2007 08:45:52 +0100
  • Delivery-date: Tue, 15 May 2007 00:42:19 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AceWxQ+7TjO4PAK4Edy09AAWy6hiGQ==
  • Thread-topic: [Xen-devel] TLB flushing in x86's map_pages_to_xen()

On 15/5/07 08:20, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> While I realize that the local-flush-only approach attempts to minimize
> overhead,
> I have some difficulty understanding how this can properly deal with the
> effects
> of speculation on remote processors. I believe this will get even worse when
> considering cacheability changes, in which case it is not only an immediate
> flush that is needed, but also an immediate cache flush.

Map_pages_to_xen() is only used at start-of-day, except for memory-guarding
where TLB flushing isn't actually required for correctness. If it were used
during normal Xen execution for more sophisticated purposes then yes, more
consideration would need to be given for flushing processor state.

 -- Keir

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