Messages in this thread | | | Date | Tue, 12 Jul 2016 13:48:06 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH 07/20] iommu/amd: Remove special mapping code for dma_ops path |
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Hi Robin,
On Tue, Jul 12, 2016 at 12:42:59PM +0100, Robin Murphy wrote: > Ah, that's the angle I was missing, yes. So if, say, someone is mapping > a page at IOVA 0x0000 while someone else is mapping a page at 0x1000, > there could still be a race between both callers writing the non-leaf > PTEs, but it's benign since they'd be writing identical entries anyway. > Seems reasonable to me (I assume in a similar map vs. unmap race, the > unmapper would just be removing the leaf entry, rather than bothering to > check for empty tables and tear down intermediate levels, so the same > still applies).
The non-leaf PTE setup code checks for races with cmpxchg, so we are on the safe side there. Two threads would write different entries there, because they are allocating differnt sub-pages, but as I said, this is checked for using cmpxchg. On the PTE level this problem does not exist.
Joerg
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