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Re: [Xen-devel] Live migration leaves page tables read-only?

Ian Pratt wrote:
Solaris implements PROT_NONE by entirely invalidating the PTE (ie. it
becomes zero). Hence our PTEs always had either zero or have the
bit set.  The only exception to this was adding some fixage to allow
for the old Xen writable page table approach which temporarily made
the upper table non-PRESENT.

So you can make not-present, but non-zero entries mean anything you
As long as it's the guest OS that creates the entries, we'll just not

Just to be confirm: in Solaris there are no not-present PTE's that
contain machine addresses.

This means we need to implement the scheme that Keir suggested to enable
the guest OS to tell xen/xc_save/restore about flags in not-present PTEs
that should trigger a m2p conversion.



Silly me. I thought "xc_linux_save" meant what it said. I haven't paid much attention to BSD or Solaris on Xen and didn't realize that went through the same path.

I'd really like to see this fixed for 3.0.4, at least for Linux, but I don't think I'm the person to implement a new "scheme" quickly to do it, but I'll try if someone wants to give me some advice on how to start.

On the subject of schemes, what about support for other architectures? Is there anything we should be thinking about for supporting guests with different page sizes, for instance?

John Byrne

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