Comment 13 for bug 531823

While I want to wait for this to further go through the process upstream, there is a fix for this issue now. And some explanation why this was observed only by some people. It seems the bug was only observable on AMD based systems which seem to need certain hypercall instructions patched where Intel CPUs do not. And that code happened to be in a write-protected section which is protected by the patch that introduced the problem.
So the fix is to allow access without checking for protections when kvm itself wants to modify an instruction. Many thanks to Marcelo Tosatti for helping on this.