Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3, Manual

Page: 334 / 1898

2:86 Volume 2, Part 1: Addressing and Protection
ld x = [b]
cmp.eq p1 = x, ‘new’
(p1) br target
...
target:
ld y = [a]
if the second processor observes the store to [b], it will also observe the store to [a].
The flush cache (
fc
,
fc.i
) instruction follows data dependency ordering.
fc
and
fc.i
are ordered only with respect to previous and subsequent load, store, or semaphore
instructions to the same line, regardless of the specified memory attribute. Subsequent
memory operations to the same line need not wait for prior
fc
or
fc.i
completion
before being globally visible.
fc
and
fc.i
are not ordered with respect to memory
operations to different lines.
mf
does not ensure visibility of
fc
and
fc.i
operations.
Instead, the
sync.i
instruction synchronizes
fc
and
fc.i
instructions, and the
sync.i
is made visible using an
mf
instruction.
4.4.8 Not a Thing Attribute (NaTPage)
A NaTPage attribute prevents non-speculative references to a page, and ensures that
speculative references to the page always defer the Data NaT Page Consumption fault.
However, as described in
“Speculation Attributes” on page 2:79 , the processor may
issue memory references to a NaTPage. As a result, all NaTPages must be backed by a
valid physical page.
Speculative or speculative advanced loads to pages marked as a NaTPage cause the
deferred exception indicator (NaT or NaTVal) to be written to the load target register,
and the memory reference is aborted. However, all other effects of the load instruction
such as post-increment are performed. Instruction fetches, loads, stores and
semaphores (including IA-32), but except for Itanium speculative loads, pages marked
as NaTPage raise a NaT Page Consumption fault.
A speculative reference to a page marked as NaTPage may still take lower priority
faults, if not explicitly deferred in the DCR.
See “Deferral of Speculative Load Faults” on
page 2:105.
4.4.9 Effects of Memory Attributes on Memory Reference
Instructions
Memory attributes affect the following Itanium instructions.
•
ldfe
,
stfe
: Hardware support for 10-byte memory accesses to a page that is
neither a cacheable page with write-back write policy nor a NaTPage is optional. On
processor implementations that do not support such accesses, an Unsupported
Data Reference Fault is raised when an unsupported reference is attempted.
For extended floating-point loads the fault is delivered only on the normal,
advanced, and check load flavors (
ldfe
,
ldfe.a
,
ldfe.c.nc
,
ldfe.c.clr
). Control
speculative flavors of the
ldfe
instruction that target pages that are not cacheable
with write-back policy always defer the fault. Refer to “Deferral of Speculative Load
Faults” on page 2:105 for details.
•
cmpxchg
and
xchg
: These instructions are only supported to cacheable pages with
write-back write policy.
cmpxchg
and
xchg
accesses to NaTPages causes a Data NaT