I dug down to the the -ENOMEM coming from the fact that the modalias is over 2KB of crap so it won't fit in the environment block when the input core tries to add it for the uevent. I don't see how it gets this way though because the MODULE_ALIAS() statement in the code just says it should be "xen: vkbd".
When I read the modalias in sysfs, it says: input:b0001v5853pFFFFe0000-e0,1,k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ramlsfw
