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Re: [Xen-devel] Swapping of PT pages

  • To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
  • From: "Mike Sun" <msun@xxxxxxxxxx>
  • Date: Wed, 20 Feb 2008 10:55:29 -0500
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 20 Feb 2008 07:55:57 -0800
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Thanks Tim, this is very interesting.  So is it safe for me to assume
that the current Linux PV implementation does not allow page table
pages to be swapped out (to ensure that it can be migrated correctly)?


> Xen is not involved in the guest's swapping/paging activities.  If a
> guest were to page its pagetables out to disk and then be migrated, they
> would indeed be incorrect when they were reloaded.  The canonicalisation
> happens only for pages that are currently in memory and marked with a
> page-table type.

> You're right.  If a guest wanted to use a pagetable after it had been
> paged out, it would have to do the same MFN->PFN canonicalization on the
> on-disk form, and PFN->MFN when reloading.
> (That's PV guests, BTW.  HVM guests that swapped their pagetables could
> potentially experience memory corruption if they used the emulated disk
> controller, but should work fine with PV drivers, or with NPT.)

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