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Re: [Xen-devel] IO-APIC pages being accessed by ACPI methods

  • To: "xen-devel" <xen-devel@xxxxxxxxxxxxx>
  • From: "Jan Beulich" <JBeulich@xxxxxxxx>
  • Date: Tue, 12 Mar 2013 10:07:21 +0000
  • Delivery-date: Tue, 12 Mar 2013 10:07:59 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

>>> On 12.03.13 at 11:00, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> If we do so (and perhaps even independently of this) we probably
> ought to enforce consistent cachability attributes on the secondary
> mappings Dom0 then is able to establish - either by further
> modifying the requested flags, or by outright denying mapping
> requests that aren't specifying UC. While the latter would be my
> preference and would work for the MMCFG case, the ACPI case
> described here wouldn't be covered - Linux'es ACPICA creates
> cachable mappings regardless of whether a SystemMemory is
> RAM or MMIO (thus risking problems even on native).

Perhaps, if the mapping request didn't specify UC, we should look
up the MTRR covering the range, and permit the mapping if the
effective cachability would nevertheless be UC. That would cover
the ACPICA case as well (as long as the firmware at least gets
the MTRRs set up correctly).


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