[RTEMS Project] #2775: ARM CP15 arm_cp15_set_translation_table_entries fails if TTB in read-only memory

[RTEMS trac]

#2775: ARM CP15 arm_cp15_set_translation_table_entries fails if TTB in read-only
memory
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 Reporter:  chrisj  |       Owner:
     Type:  defect  |      Status:  new
 Priority:  normal  |   Milestone:  4.12
Component:  libcpu  |     Version:  4.12
 Severity:  normal  |  Resolution:
 Keywords:  ARM     |
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Comment (by ppisa):

 I think that disabling of MMU at runtime is highly problematic. You need
 to stop all parallel processes to ensure that all modifications held in
 cache are propagated to memory and then switch MMU off. If multiple CPUs
 are running (SMP) then there is almost no way hot to ensure fully
 synchronized case for at least some ARM architecture members. Coherency is
 maintained through MMU and guaranteed only for cache clean through VMA.
 The cache clean by level+set+way does not need to generate required snoop
 operations.

 On the other hand, ARM architecture is prepared and operations are
 optimized for runtime page tables updates and switching and there are
 defined operations sequences to ensure correct page tables changes
 propagations in ARM architecture manuals. So I vote for this direction.

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Ticket URL: <http://devel.rtems.org/ticket/2775#comment:1>
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