On Thu, Nov 09, 2023 at 01:21:59PM +0000, Joao Martins wrote: > On 09/11/2023 13:09, Jason Gunthorpe wrote: > > On Thu, Nov 09, 2023 at 01:03:02PM +0000, Joao Martins wrote: > > > >>> I am not talking about mdevs; but rather the regular (non mdev) case not > >>> being > >>> able to use dirty tracking with autodomains hwpt allocation. > >> > >> ... without any vIOMMU. > > > > Ah, well, that is troublesome isn't it.. > > > > So do we teach autodomains to be more featured in the kernel or do we > > teach the generic qemu code to effectively implement autodomains in > > userspace? > > The latter is actually what we have been doing. Well I wouldn't call > autodomains > in qemu, but rather just allocate a hwpt, instead of attaching the IOAS > directly. But well mdevs don't have domains and we overlooked that. I would > turn > the exception into an exception rather than making the norm, doesn't look to > be > much complexity added?
Autodomains are complex because of things like mdev and iommu non-uniformity's. Qemu can't just allocate a single HWPT, it needs to be annoyingly managed. > What I last re-collect is that autodomains represents the 'simple users' that > don't care much beyond the basics of IOMMU features (I recall the example was > DPDK apps and the like). You could say that for current needs IOMMU > autodomains > suffices for qemu. Yes, that was my intention. Aside from that it primarily exists to support vfio compatibility > Connecting autodomains to this enforcing on the hwpt is relatively simple btw, > it just needs to connect the dirty tracking flag with same semantic of > hwpt-alloc equivalent and pass the hwpt flags into the domain allocation. Yes > It's more of what of a question should be the expectations to the user when > using ATTACH_HWPT with an IOAS_ID versus direct manipulation of HWPT. I am > wondering if dirty tracking is alone here or whether there's more features > that > start to mud the simplicity of autodomains that would approximate of > hwpt-alloc. This is why I had been thinking of a pure HWPT based scheme So it seems we cannot have a simple model where the generic qmeu layer just works in IOAS :( It might as well always work in HWPT and understand all the auto domains complexity itself. Jason
