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[Xen-devel] RE: Why "Don't use shadow linear maps in sh_set_toplevel_shadow"?


  • To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>
  • From: "Li, Xin B" <xin.b.li@xxxxxxxxx>
  • Date: Fri, 17 Nov 2006 23:47:51 +0800
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 17 Nov 2006 07:48:15 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AccKXggJW0JGyMm+RWKukaZn6SY0hQAAKpQw
  • Thread-topic: Why "Don't use shadow linear maps in sh_set_toplevel_shadow"?

>At 23:13 +0800 on 17 Nov (1163805188), Li, Xin B wrote:
>> It's changeset 12399, but can not understand, can you pls explain?
>
>Because we can't use the shadow linear maps before we build them. 
>The top-level shadow entry is explicitly null during that routine, and
>the writeable-mappings heuristics use the shadow linear map, so it's
>not safe to use them there. 
>

Not understand.
writing a new cr3 means a context switch, guest kernel address space
should be still accessible during the switching, so it seems OK to me to
use the heuristics.
And what do you mean by "safe"?
thanks
-Xin

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