Hi Jason, On Thu, 13 May 2021 19:31:22 -0300, Jason Gunthorpe <[email protected]> wrote:
> On Thu, May 13, 2021 at 01:22:51PM -0700, Jacob Pan wrote: > > Hi Tony, > > > > On Thu, 13 May 2021 12:57:49 -0700, "Luck, Tony" <[email protected]> > > wrote: > > > > > On Thu, May 13, 2021 at 12:46:21PM -0700, Jacob Pan wrote: > > > > It seems there are two options: > > > > 1. Add a new IOMMU API to set up a system PASID with a *separate* > > > > IOMMU page table/domain, mark the device is PASID only with a flag. > > > > Use DMA APIs to explicit map/unmap. Based on this PASID-only flag, > > > > Vendor IOMMU driver will decide whether to use system PASID domain > > > > during map/unmap. Not clear if we also need to make IOVA==kernel VA. > > > > > > > > 2. Add a new IOMMU API to setup a system PASID which points to > > > > init_mm.pgd. This API only allows trusted device to bind with the > > > > system PASID at its own risk. There is no need for DMA API. This is > > > > the same as the current code except with an explicit API. > > > > > > > > Which option? > > > > > > Option #1 looks cleaner to me. Option #2 gives access to bits > > > of memory that the users of system PASID shouldn't ever need > > > to touch ... just map regions of memory that the kernel has > > > a "struct page" for. > > > > > > What does "use DMA APIs to explicitly map/unmap" mean? Is that > > > for the whole region? > > > > > If we map the entire kernel direct map during system PASID setup, then > > we don't need to use DMA API to map/unmap certain range. > > > > I was thinking this system PASID page table could be on-demand. The > > mapping is built by explicit use of DMA map/unmap APIs. > > Option 1 should be the PASID works exactly like a normal RID and uses > all the normal DMA APIs and IOMMU mechanisms, whatever the platform > implements. This might mean an iommu update on every operation or not. > > > > I'm expecting that once this system PASID has been initialized, > > > then any accelerator device with a kernel use case would use the > > > same PASID. I.e. DSA for page clearing, IAX for ZSwap compression > > > & decompression, etc. > > > > > OK, sounds like we have to map the entire kernel VA with struct page as > > you said. So we still by-pass DMA APIs, can we all agree on that? > > Option 2 should be the faster option, but not available in all cases. > > Option 1 isn't optional. DMA and IOMMU code has to be portable and > this is the portable API. > > If you want to do option 1 and option 2 then give it a go, but in most > common cases with the IOMMU in a direct map you shouldn't get a > notable performance win. > Looks like we are converging. Let me summarize the takeaways: 1. Remove IOMMU_SVA_BIND_SUPERVISOR flag from this patch, in fact there will be no flags at all for iommu_sva_bind_device() 2. Remove all supervisor SVA related vt-d, idxd code. 3. Create API iommu_setup_system_pasid_direct_map(option_flag) if (option_flag == 1) iommu_domain_alloc(IOMMU_DOMAIN_DMA); if (option_flag == 2) iommu_domain_alloc(IOMMU_DOMAIN_DIRECT); //new domain type? setup IOMMU page tables mirroring the direct map 4. Create API iommu_enable_dev_direct_map(struct dev, &pasid, &option) - Drivers call this API to get the system PASID and which option is available on the system PASID - mark device as PASID only, perhaps a new flag in struct device->dev_iommu->pasid_only = 1 5. DMA API IOMMU vendor ops will take action based on the pasid_only flag to decide if the mapping is for system PASID page tables. Does it make sense? > Jason Thanks, Jacob _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
