On Fri, Apr 03, 2020 at 07:38:11PM +1100, Alexey Kardashevskiy wrote: > > > On 26/03/2020 12:26, Alexey Kardashevskiy wrote: > > > > > > On 25/03/2020 19:37, Christoph Hellwig wrote: > >> On Wed, Mar 25, 2020 at 03:51:36PM +1100, Alexey Kardashevskiy wrote: > >>>>> This is for persistent memory which you can DMA to/from but yet it does > >>>>> not appear in the system as a normal memory and therefore requires > >>>>> special handling anyway (O_DIRECT or DAX, I do not know the exact > >>>>> mechanics). All other devices in the system should just run as usual, > >>>>> i.e. use 1:1 mapping if possible. > >>>> > >>>> On other systems (x86 and arm) pmem as long as it is page backed does > >>>> not require any special handling. This must be some weird way powerpc > >>>> fucked up again, and I suspect you'll have to suffer from it. > >>> > >>> > >>> It does not matter if it is backed by pages or not, the problem may also > >>> appear if we wanted for example p2p PCI via IOMMU (between PHBs) and > >>> MMIO might be mapped way too high in the system address space and make > >>> 1:1 impossible. > >> > >> How can it be mapped too high for a direct mapping with a 64-bit DMA > >> mask? > > > > The window size is limited and often it is not even sparse. It requires > > an 8 byte entry per an IOMMU page (which is most commonly is 64k max) so > > 1TB limit (a guest RAM size) is a quite real thing. MMIO is mapped to > > guest physical address space outside of this 1TB (on PPC). > > > > > > I am trying now this approach on top of yours "dma-bypass.3" (it is > "wip", needs an upper boundary check): > > https://github.com/aik/linux/commit/49d73c7771e3f6054804f6cfa80b4e320111662d > > Do you see any serious problem with this approach? Thanks!
Do you have a link to the whole branch? The github UI is unfortunately unusable for that (or I'm missing something). _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu