Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 687

PAL_MEMORY_BUFFER
A memory buffer must be allocated for each physical package, and is shared by all
logical processors on that package. Software is required to call this procedure on all
logical processors on a given package with the same input values. If not, processor
operation is undefined.
If the PAL reset hand-off state indicates that the memory buffer is required but no call
is made to allocate the memory buffer for a given physical package before calling
buffer-dependent PAL procedures on a logical processor on that package, those
procedures return an error.
If software would like to relocate this memory buffer at a later point in time, it can do
so by setting the value of reg field in control_word to one. PAL will copy the contents of
the existing buffer to a new buffer. Software is still required to make this call on all
logical processors with the same input arguments when relocating the buffer. Once the
call has been made on all logical processors in the physical package, the old memory
can be reclaimed.
Software can choose if it wants this procedure to periodically poll for interrupts during
the execution of the procedure. If an interrupt is seen, the procedure will return a value
of 1 and software must re-call this procedure again on the same logical processor, with
the same input arguments, until the copy is completed. If this procedure returns with a
value of 1, both the old memory buffer and the new memory buffer will be in use by
PAL until PAL returns that the procedure has completed execution successfully by
setting the return value to 0.
An error will be returned if software calls this procedure with the reg value set to one to
re-register a buffer and a call has never been made to register the buffer.
It is required that PAL firmware only perform cacheable memory accesses to this buffer.
Volume 2, Part 1: Processor Abstraction Layer 2:439