HVM guests are able to manipulate their physical address space such that processing a subsequent request by that guest to disable caches takes an extended amount of time changing the cachability of the memory pages assigned to this guest. This applies only when the guest has been granted access to some memory mapped I/O region (typically by way of assigning a passthrough PCI device). This can cause the CPU which processes the request to become unavailable, possibly causing the hypervisor or a guest kernel (including the domain 0 one) to halt itself ("panic"). A malicious domain, given access to a device with memory mapped I/O regions, can cause the host to become unresponsive for a period of time, potentially leading to a DoS affecting the whole system. Only systems using the Intel variant of Hardware Assisted Paging (aka EPT) are vulnerable. Acknowledgements: Red Hat would like to thank the Xen for reporting this issue. Upstream acknowledges Zhenzhong Duan as the original reporter.
Statement: Not vulnerable. This issue did not affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5. This issue did not affect the versions of the Linux kernel as shipped with Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG as we did not have support for Xen hypervisor.
Now public via: http://seclists.org/oss-sec/2013/q3/182
Created xen tracking bugs for this issue: Affects: fedora-all [bug 987914]