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WARNING
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LINE
154,
SEGIHHT
CDHTAIHS
PRIVILEGED INSTRUCTIOHS
55
ud
Figure 11-3. Example
of
NPX
Context
Switching
When a program changes a descriptor that
is
shared with other processors, it should broadcast this fact
to
the other processors. This broadcasting can
be
done with
.an
inter-processor inierrupl. Tht;
hiii,;11;;,
for this interrupt must ensure that the segment registers, the LDTR and the TR, are re-Ioaded. This
happens automatically if the interrupt
is
serviced by a.task switch.
Modification of descriptors of shared segments in multi-processor systems
may
require that the on-chip
descriptors also
be
updated. For example,
one
processor may attempt
to
mark the descriptor of a shared
segment
as
not-present while another
is
using it. Software has
to
ensure that the descriptors
in
the
segment register caches are updated with the
new
information. The segment register caches can
be
11-6