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cc4b7c1814
When we replace an SLB entry in the MFC after using up all the available entries, there is a short window in which an incorrect entry is marked as valid. The problem is that the 'valid' bit is stored in the ESID, which is always written after the VSID. Overwriting the VSID first will make the original ESID entry point to the new VSID, which means that any concurrent DMA accessing the old ESID ends up being redirected to the new virtual address. A few cycles later, we write the new ESID and everything is fine again. That race can be closed by writing a zero entry to the ESID first, which makes sure that the VSID is not accessed until we write the new ESID. Note that we don't actually need to invalidate the SLB entry using the invalidation register, which would also flush any ERAT entries for that segment, because the segment translation does not become invalid but is only removed from the SLB cache. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Jeremy Kerr <jk@ozlabs.org> |
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