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RE: [Xen-devel] [PATCH][SVM] fix pae for guests on 32bit HV

To: "Woller, Thomas" <thomas.woller@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH][SVM] fix pae for guests on 32bit HV
From: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Date: Thu, 20 Apr 2006 16:01:33 -0700
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Thread-topic: [Xen-devel] [PATCH][SVM] fix pae for guests on 32bit HV
Woller, Thomas wrote:
>> The current shadow code does not support PAE guests on the
>> PAE Xen. It's much harder given (compared with x64-64) the limited
>> bits in page_info. Should work on the 64-bit Xen. Anyway, we need to
>> cleanly kill such guests on the PAE Xen.
> Now this does mean no NX support on PAE xen.

That's right. 

> Attached patch simply turns off PAE if paging level < 4 in vt and svm.

Actually it would cause a hang with bigsmp Linux; we debugged such
guests. Such a PAE-confugred Linux checks PAE when paging level = 2, and
stop booting if PAE is not available.

Our solution was to disable pae (the default) in the xm config file.

> Tested win2003 EE on svm and vt, allows 32bit windows guests to boot
> without shadow.c bug() crash.
> Only issue seen is if setting guest config memory >~4096 then the
> guest does not boot, but does not crash the hv - stays in blocked
> state.  So, I think that this solution is fine for now.  Svm shadows
> PAE and NX so the code is slightly different.
> I'll post with signed-off if ok for vmx also.
> thanks
> Tom

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