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[Xen-devel] Signalling DomU on TPR write

  • To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
  • Date: Thu, 1 Jan 2009 11:57:37 +1100
  • Delivery-date: Wed, 31 Dec 2008 16:58:06 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Aclrq/CHzsnJS6rURJmB2SpgYv3Pew==
  • Thread-topic: Signalling DomU on TPR write

Keir (and anyone else with an opinion on this :),

Given that you have suggested that patching from the hypervisor might
have synchronisation issues, my current thought on a mechanism for
signalling a DomU when a TPR write occurs is this:

. DomU allocates a page and makes a hypercall to the hypervisor saying
"put info about TPR writes here" and use this event channel to signal

. When a TPR write occurs, the hypervisor fills in the entry in the
buffer nominated above and sets a flag. Until the flag is cleared, the
hypervisor does no further signalling.

. The guest sees the event (via the interrupt - same as any other
event), patches the kernel as appropriate, then clears the flag

. Repeat until all the places are patched.

Obviously a number of iterations will be required before all the
patching is done, but I don't think that's a problem. Patching would
occur in the DomU with all processors at HIGH_LEVEL (interrupts

Does that sound acceptable?



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