some question about TCR setting

vichy vichy.kuo at
Sun Nov 16 18:37:18 PST 2014

hi Russel:
>> if those page tables are not mapped into the virtual address space,
>> how OS create them?
>> (AFAIK, once System.M is enabled, the processor cannot access where
>> page table doesn't map to)
>> except those page tables are created before System.M enabled.
> The OS temporarily maps the page tables into virtual space to update
> them.  Once updated, the OS unmaps the page tables.
> However, forget this detail - the MMU page table walker knows nothing
> about the virtual address space: MMU page table walks do not happen in
> the virtual address space, they happen in the physical address space.
> So, it makes no odds what so ever whether the table is mapped or not.

For some processors, if the type of L1 cache is VIPT, does that mean
MMU page table will not be cached in this level of cache?

>> BTW, why we need to set page table walk attribute as sharable and
>> inner/outer cacheable?
> The access type is included on the bus along with the address and other
> attributes.  This includes whether it's sharable, and the cache attributes.
> A MMU page walker may be implemented such that it is capable of accessing
> L2 cache.
> In that case, we would want the MMU page walker to be able to read from
> the L2 cache, which would need the access to be marked as "normal memory,
> cacheable" so that the cache is searched for a matching line.  This in
> turn means that software does not have to flush page table updates all
> the way back to the physical memory - merely flushing them out of the L1
> cache is sufficient.
so Inner/outer attributes are use to determine whether it is cached in
L1 or L2 cache, right?
how about sharable?
AFAIK, sharable means for a particular domain it requires hardware to
ensure that
the location is coherent for all agents in that domain.
Since page table is unique to each processor, why we need to share it
between other cores?

Sincerely Appreciate your kind help,

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