[Linux-ia64] [RFC] NUMA functions for accessing replicated areas

[Keith Owens <kaos@ocs.com.au>]

The linux kernel debugger (kdb) has hit a problem with setting software
breakpoints on NUMA boxes with replicated kernel text.  Instead of
changing one kernel virtual address and affecting the only copy of the
kernel, kdb has to loop over each replicated area and change each copy
of the kernel individually, using some mapping that gives access to the
data on other nodes.

I don't want code in kdb that knows about every NUMA platform, that is
a maintenance nightmare.  I want the NUMA platforms to provide the
following interfaces.  Any objections or changes?  I will do the the
SGI version, other manufacturers will have to provide the equivalent
functions if they want to use kdb.

BTW, is there a single NUMA mailing list?  cc: me please, I am not on
all lists.

CONFIG_NUMA_REPLICATE

  Set to y if the platform supports the replication functions.

int numa_replicated(unsigned long address, size)

  Return 0 if the area (address to address+size-1) is not replicated.
  Return 1 if it is replicated.
  Return -EINVAL if the area is a mixture of replicated and
  non-replicated data.

int numa_replicate_loop(unsigned long address, (int *func)(void *numadata, void *funcdata), void *funcdata)

  Call the function for each replication of the address.  numadata
  identifies this instance of the replicated data, it is an opaque
  cookie to the function.  funcdata is supplied by the caller of
  numa_replicate_loop(), it is an opaque cookie to the numa code.

  Return 0 if the function returns 0 for all calls, otherwise 1.  If
  any call to func() returns non-zero, numa_replicate_loop() continues
  with the other replicated areas.  If func() wants to ignore
  subsequent areas it can set a flag in funcdata.

int numa_replicate_getarea_size(void *to, unsigned long from_xxx, size_t size, void *numadata)

  Read size bytes from from_xxx (which must be a replicated address) to
  the user's data area.

  Return 0 on success, -EFAULT for invalid from_xxx address or size.

int numa_replicate_putarea_size(unsigned long to_xxx, void *from, size_t size, void *numadata)

  Write size bytes from the user's data area to to_xxx (which must be a
  replicated address).

  Return 0 on success, -EFAULT for invalid to_xxx address or size.

Is that satisfactory?  Once those routines exist, kdb can use them to
set software breakpoints.