The XSA on Spectre/Meltdown has been updated again, with more info on ARM firmware:
Xen Security Advisory CVE-2017-5753,CVE-2017-5715,CVE-2017-5754 / XSA-254
Information leak via side effects of speculative execution
UPDATES IN VERSION 12:
Corrections to ARM SP2 information:
* ARM 32-bit requires new firmware on some CPUs.
* Provide link to the ARM firmware page, accordingly.
* ARM 32-bit mitigations are complete for Cortex-A CPUs.
We do not have information for other ARM CPUs at this time.
Systems running all versions of Xen are affected. For SP1 and SP2, both Intel and AMD are vulnerable. Vulnerability of ARM processors to SP1 and SP2 varies by model and manufacturer. ARM has information on affected models on the following website. For SP3, only Intel processors are vulnerable. (The hypervisor cannot be attacked using SP3 on any ARM processors, even those that are listed as affected by SP3.) Furthermore, only 64-bit PV guests can exploit SP3 against Xen. PVH, HVM, and 32-bit PV guests cannot exploit SP3.