Hi Maxime, 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. > > > + *pte_addr = sun50i_mk_pte(paddr, prot); > > > + sun50i_table_flush(sun50i_domain, pte_addr, 1); > > > > This maps only one page, right? But the function needs to map up to > > 'size' as given in the parameter list. > > It does, but pgsize_bitmap is set to 4k only (since the hardware only > supports that), so we would have multiple calls to map, each time with > a single page judging from: > https://elixir.bootlin.com/linux/latest/source/drivers/iommu/iommu.c#L1948 > > Right? Okay, you are right here. Just note that when this function is called for every 4k page it should better be fast and avoid slow things like TLB flushes. > The vendor driver was doing something along those lines and I wanted > to be conservative with the cache management if we didn't run into > performances issues, but I'll convert to the iotlb callbacks then. Yeah, that definitly helps performance. Regards, Joerg
