Hi, On Wed, Apr 08, 2020 at 04:06:49PM +0200, Joerg Roedel wrote: > On Wed, Apr 01, 2020 at 01:47:10PM +0200, Maxime Ripard wrote: > > As far as I understand it, the page table can be accessed concurrently > > since the framework doesn't seem to provide any serialization / > > locking, shouldn't we have some locks to prevent concurrent access? > > The dma-iommu code makes sure that there are no concurrent accesses to > the same address-range of the page-table, but there can (and will) be > concurrent accesses to the same page-table, just for different parts of > the address space. > > Making this lock-less usually involves updating non-leaf page-table > entries using atomic compare-exchange instructions. That makes sense, thanks! I'm not sure what I should compare with though, do you want to compare with 0 to check if there's already a page table assigned to that DTE? If so, then we should also allocate the possible page table before the fact so that we have something to swap with, and deallocate it if we already had one? Maxime
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