[PATCH] powerpc: kdump: Reserve the existing TCE mappings left by the first kernel

[Haren Myneni]

Paul, Olof,

tce_union got removed in powerpc.git tree. Hence reposting the patch 
created against this tree. This patch is implemented based on Olof's 
suggestion of reserving TCE entries and use only available ones in the 
kdump boot and tested on P5, P4, JS20 and JS21 machines.

If you are OK with this patch, please send it to upstream.

Thanks
Haren

During kdump boot, noticed some machines checkstop on dma protection 
fault for ongoing DMA left in the first kernel. Instead of initializing 
TCE entries in iommu_init() for the kdump boot, this patch fixes this 
issue by walking through the each TCE table and checks whether the 
entries are in use by the first kernel. If so, reserve those entries by 
setting the corresponding bit in tbl->it_map such that these entries 
will not be available for the kdump boot.

However it could be possible that all TCE entries might be used up due 
to the driver bug that does continuous mapping. My observation is around 
1700 TCE  entries are used on some systems (Ex: P4) at some point of 
time during kdump boot and saving dump (either write into the disk or 
sending to remote machine). Hence, this patch will make sure that 
minimum of 2048 entries will be available such that kdump boot could be 
successful in some cases.

Signed-off-by: Haren Myneni <haren at us.ibm.com>


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