On Tue, Dec 15, 2015 at 09:53:18AM -0700, Alex Williamson wrote: > On Tue, 2015-12-15 at 13:43 +0000, O'Driscoll, Tim wrote: > > > -----Original Message----- > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Alex > > > Williamson > > > Sent: Friday, December 11, 2015 11:03 PM > > > To: Vincent JARDIN; dev at dpdk.org > > > Subject: Re: [dpdk-dev] VFIO no-iommu > > > > > > On Fri, 2015-12-11 at 23:12 +0100, Vincent JARDIN wrote: > > > > Thanks Thomas for putting back this topic. > > > > > > > > Alex, > > > > > > > > I'd like to hear more about the impacts of "unsupported": > > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/c > > > > ommi > > > > t/?id=033291eccbdb1b70ffc02641edae19ac825dc75d > > > > ???Use of this mode, specifically binding a device without a > > > > native > > > > ???IOMMU group to a VFIO bus driver will taint the kernel and > > > > should > > > > ???therefore not be considered supported. > > > > > > > > It means that we get ride of uio; so it is a nice code cleanup: > > > > but > > > > why > > > > would VFIO/NO IOMMU be better if the bottomline is "unsupported"? > > > > > > How supportable do you think the uio method is? ?Fundamentally we > > > have > > > a userspace driver doing unrestricted DMA; it can access and modify > > > any > > > memory in the system. ?This is the reason uio won't provide a > > > mechanism > > > to enable MSI and if you ask the uio maintainer, they don't support > > > DMA > > > at all, it's only intended as a programmed IO interface to the > > > device. > > > ?Unless we can sandbox a user owned device within an IOMMU > > > protected > > > container, it's not supportable. ?The VFIO no-iommu mode can simply > > > provide you that unsupported mode more easily since it leverages > > > code > > > from the supported mode, which is IOMMU protected. ?Thanks, > > > > Thanks for clarifying. > > > > This does seem like it would be useful for DPDK. We're doing some > > further investigation to see if it works out of the box with DPDK or > > if we need to make any changes to support it. > > The iommu model is different, there's no type1 interface available when > using this mode since we have no ability to provide translation. ?The > no-iommu iommu model really does nothing, which is a possible issue for > userspace. ?Is it sufficient? ?We stopped short of creating a page > pinning interface through the no-iommu model because it requires code > and adding piles of new code for an interface we claim is unsupported > doesn't make a lot of sense. ?The device interface should be identical > to existing vfio support. > > > Thomas highlighted that your original commit for this had been > > reverted. What specifically would you need from us in order to re- > > submit the VFIO No-IOMMU support? > > No API changes should ever go into the kernel without being validated > by a user. ?Without that we're risking that the kernel interface is > broken and we're stuck supporting it. ?In this case I tried to make > sure we had a working user before it went it, gambled that it was close > enough to put in anyway, then paid the price when development went > silent on the user side. ?To get it back in, I'm going to need a > working use first. ?You can re-apply 033291eccbdb or re- > revert?ae5515d66362 for development of that. ?I need to see that it > works and that there's some consensus from the dpdk community that it's > a worthwhile path forward for cases without an iommu. ?There's no point > in merging it if it only becomes a userspace proof of concept. ?Thanks, > I tested the DPDK (HEAD of master) with the patch, with help of Anatoly, and DPDK works in no-iommu environment with a little modification.
Basically the only modification is adapt new group naming (noiommu-$) and disable dma mapping (VFIO_IOMMU_MAP_DMA) Also I need to disable VFIO_CHECK_EXTENSION ioctl, because in vfio module, container->noiommu is not set before doing a vfio_group_set_container() and vfio_for_each_iommu_driver selects wrong driver. What I test is bind two different type of NICs into VFIO driver, and use testpmd to confirm transfer is working. Kernel booted without iommu enabled, vfio module inserted with "enable_unsafe_noiommu_support" parameter. Thanks, ferruh
