RE: [Xen-devel] [PATCH] Included reserved memory regions in dom0 iommu mappings

[Ross Philipson <Ross.Philipson@xxxxxxxxxx>]

Agreed. Bear in mind it is a workaround just for some cases we have seen. But 
yes if there are reserved ranges beyond the highest E820_RAM type in the memory 
map then they would still be excluded. The workaround could be extended to add 
these but I guess where does the working around end. For example I got an email 
yesterday from someone who has a really broken BIOS where the RMRR end 
addresses are higher than the start addresses. The patch can't help here either.

Thanks
Ross

-----Original Message-----
From: Cui, Dexuan [mailto:dexuan.cui@xxxxxxxxx] 
Sent: Thursday, February 26, 2009 4:20 AM
To: Ross Philipson; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] [PATCH] Included reserved memory regions in dom0 iommu 
mappings

The patch is useful when BIOS doesn’t report RMRR correctly; however the patch 
may not help in some situations.
E.g., to work around a buggy BIOS, we may have to map such an E820 entry
(XEN)  00000000cff0b000 - 00000000d0000000 (reserved).
But if we use a xen parameter "mem=512m", or, if the host only has 512m memory, 
the variable 'max_page" is 512m/PAGE_SIZE, so even with the patch, the E820 
entry would not be mapped, and Xen would still hang.

-- Dexuan

________________________________________
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ross Philipson
Sent: 2009年2月24日 4:01
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH] Included reserved memory regions in dom0 iommu 
mappings

This adds a boolean boot parameter to xen to allow reserved memory
regions to be added to the iommu mappings for dom0. The parameter
is "iommu_include_reserved" and is off by default. A warning is
also traced when incorrect RMRR to system memory map values are
detected. This is being added to address some incorrect BIOS's that 
do not report correctly the requied reserved memory ranges in 
the RMRRs. When this occurs it currently can cause early boot hangs
and crashes.

Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxx>

Based on changeset 19238

Thanks
Ross


Ross Philipson
Senior Software Engineer
Citrix Systems, Inc
14 Crosby Drive
Bedford, MA 01730
781-301-7949
ross.philipson@xxxxxxxxxx


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