Trace buffers no longer working -- What changed?

[Rob Gardner <rob.gardner@hp.com>]

It has come to my attention that Xenmon and xentrace have stopped 
working in the latest xen-unstable tree, but I'm not sure precisely when 
this happened. The problem is that both utilities are failing to map the 
xen trace buffers into user space. Anyone have any idea what might have 
changed recently that could have caused this? The trace buffer 
allocation code in the hypervisor is using alloc_xenheap_pages() 
followed by SHARE_PFN_WITH_DOMAIN(), and then the userland apps use 
xc_map_foreign_range() to get access to the trace buffers. 
xc_map_foreign_range() uses ioctl(IOCTL_PRIVCMD_MMAP) which is failing 
with errno 14 (bad address). In particular, the privcmd ioctl uses 
direct_remap_pfn_range() which is actually returning the error. I kind 
of suspect that there's nothing wrong at the userland side of things, 
but something is going wrong when the memory is allocated and "shared". 
Can anybody help?

Rob