Bug 218820 - HVM guests limited to 2G memory
HVM guests limited to 2G memory
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: xen (Show other bugs)
All Linux
medium Severity medium
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Assigned To: Xen Maintainance List
: Reopened
Depends On: 218822
Blocks: 197865
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Reported: 2006-12-07 13:13 EST by Stephen Tweedie
Modified: 2010-10-22 03:20 EDT (History)
2 users (show)

See Also:
Fixed In Version: RHEA-2007-0635
Doc Type: Bug Fix
Doc Text:
At present, the Virtualization feature has the following limitations: * Virtualized kernels cannot support suspend / resume capabilities. * Hardware-virtualized guests cannot have more than 2GB of RAM.
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Last Closed: 2007-11-07 12:08:53 EST
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RHEL 7.3 requirements from Atomic Host:
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Description Stephen Tweedie 2006-12-07 13:13:32 EST
From upstream:

> On IA32 host or IA32 PAE host, at present, generally, we can't create an
> HVM guest with more than 2G memory, because generally it's almost
> impossible for Qemu to find a large enough and consecutive virtual
> address space to map an HVM guest's whole physical address space.
> The attached patch fixes this issue using dynamic mapping based on
> little blocks of memory.
Comment 1 Stephen Tweedie 2006-12-07 13:15:16 EST
Upstream thread/patch is at


for now, we should document the 2G limit.
Comment 2 Daniel Berrange 2006-12-07 13:23:16 EST
NB, the patch from that thread has other implications - it will expose a PAE bug
in the HV  shadow code which was not previously hit. See bug 218822

Comment 3 Don Domingo 2006-12-07 23:06:28 EST
added to release notes (under "Virtualization"):

At present, the Virtualization feature has the following limitations:

    * Virtualized kernels cannot support suspend / resume capabilities.
    * Hardware-virtualized guests cannot have more than 2GB of RAM.

above note will be included in RC Release notes. kindly inform me if any
revisions are in order.

<making this bug block release notes, for tracking purposes>
Comment 4 Stephen Tweedie 2006-12-19 21:25:25 EST
2GB limit is believed to be x86 only; on x86_64, up to 4GB should work, and we
are investigating raising those limits for future updates.
Comment 7 Jay Turner 2007-01-19 08:45:15 EST
Closing out.  Please ensure that a 5.1 bug is entered to track resolution of the
original issue.
Comment 9 RHEL Product and Program Management 2007-03-21 19:26:55 EDT
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release.  Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products.  This request is not yet committed for inclusion in an Update
Comment 10 Rik van Riel 2007-03-26 17:48:29 EDT
This bug is not easily fixable and should probably be documentation only.

The problem is that qemu-dm maps all of a guest domain's memory, so more than
2GB simply won't fit in a 32 bit host.

A 64 bit host should be able to deal with larger 32bit HVM guests, this needs to
be tested.
Comment 13 Daniel Berrange 2007-06-20 11:02:59 EDT
The patches we believe we need to resolve this bug are all brought in as part of
the 3.1  hypervisor / qemu rebase. Switching this bug to MODIFIED, since QA has
the only hardware with enough memory to really test this.
Comment 16 errata-xmlrpc 2007-11-07 12:08:53 EST
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

Comment 18 Don Domingo 2008-08-12 01:23:10 EDT
Release note added. If any revisions are required, please set the 
"requires_release_notes" flag to "?" and edit the "Release Notes" field accordingly.
All revisions will be proofread by the Engineering Content Services team.

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