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Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking

To: Alex Williamson <alex.williamson@xxxxxx>
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Tue, 9 Mar 2010 17:22:29 -0500
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>, Weidong Han <weidong.han@xxxxxxxxx>, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "linux@xxxxxxxxxxxxxx" <linux@xxxxxxxxxxxxxx>, "keir.fraser@xxxxxxxxxxxxx" <keir.fraser@xxxxxxxxxxxxx>
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On Tue, Mar 09, 2010 at 02:57:00PM -0700, Alex Williamson wrote:
> On Tue, Mar 9, 2010 at 2:30 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Tue, Mar 09, 2010 at 02:39:10PM -0700, Alex Williamson wrote:
> >>
> >> I have a system with what I consider to be a valid DRHD that's getting
> >> tripped up on this patch.  The problem is that the DRHD includes an
> >> IOAPIC scope, where the IOAPIC is not materialized on the PCI bus.  I
> >> think Xen is being overzealous in it's validity checking and that this
> >> is a valid configuration.  What do others think?  Are IOAPICs a
> >
> > How does upstream Linux handle this?
> Last I checked, it works just fine, doesn't care that the IOAPIC isn't
> materialized.

This is from drivers/pci/intr_remapping.c (2.6.34-rc0):

795         if (ir_supported && ir_ioapic_num != nr_ioapics) {
796                 printk(KERN_WARNING
797                        "Not all IO-APIC's listed under remapping
798                 return -1;
799         }

ir_ioapic_num is figured out from the count of DRHD's.

So I think Linux would actually turn off VT-d.

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