Hi Jean-Philippe, On Thu, Oct 12, 2017 at 12:13:20PM +0100, Jean-Philippe Brucker wrote: > On 11/10/17 12:33, Joerg Roedel wrote: > > Here is how I think the base API should look like: > > > > * iommu_iovm_device_init(struct device *dev); > > iommu_iovm_device_shutdown(struct device *dev); > > > > These two functions do the device specific setup/shutdown. For > > PCI this would include enabling the PRI, PASID, and ATS > > capabilities and setting up a PASID table for the device. > > Ok. On SMMU the PASID table also hosts the non-PASID page table pointer, > so the table and capability cannot be setup later than attach_device (and > we'll probably have to enable PASID in add_device). But I suppose it's an > implementation detail. Right, when the capabilities are enabled is an implementation detail of the iommu-drivers. > Some device drivers will want to use ATS alone, for accelerating IOVA > traffic. Should we enable it automatically, or provide device drivers with > a way to enable it manually? According to the PCI spec, PASID has to be > enabled before ATS, so device_init would have to first disable ATS in that > case. Yes, driver can enable ATS for normal use of a device, and disable/re-enable it when the driver requests PASID/PRI functionality. That is also an implementation detail. You should probably also document that the init/shutdown functions may interrupt device operation, so that driver writers are aware of that. > > > * iommu_iovm_bind_mm(struct device *dev, struct mm_struct *mm, > > iovm_shutdown_cb *cb); > > iommu_iovm_unbind_mm(struct device *dev, struct mm_struct *mm); > > > > These functions add and delete the entries in the PASID table > > for the device and setup mmu_notifiers for the mm_struct to > > keep IOMMU TLBs in sync with the CPU TLBs. > > > > The shutdown_cb is invoked by the IOMMU core code when the > > mm_struct goes away, for example because the process > > segfaults. > > > > The PASID handling is best done these functions as well, unless > > there is a strong reason to allow device drivers to do the > > handling themselves. > > > > The context data can be stored directly in mm_struct, including the > > PASID for that mm. > > Changing mm_struct probably isn't required at the moment, since the mm > subsystem won't use the context data or the PASID. Outside of > drivers/iommu/, only the caller of bind_mm needs the PASID in order to > program it into the device. The only advantage I see would be slightly > faster bind(), when finding out if a mm is already bound to devices. But > we don't really need fast bind(), so I don't think we'd have enough > material to argue for a change in mm_struct. The idea behind storing the PASID in mm_struct is that we have a system-wide PASID-allocator and only one PASID per address space, even when accessed from multiple devices. There will be hardware implemenations where this is required, afaik. It doesn't mean that it _needs_ to be part of mm_struct, but it is certainly easier than tracking this 1-1 relation separatly. > We do need to allocate a separate "iommu_mm_struct" wrapper to store the > mmu_notifier. Maybe bind() could return this structure (that contains the > PASID), and unbind() would take this iommu_mm_struct as argument? I'd like to track this iommu_mm_struct only in iommu-code, otherwise drivers need to track the pointer somewhere. And we need to track the mm_struct->iommu_mm_struct relation anyway in core-code to handle events like segfaults, when the whole mm_struct goes away under us. So when we track this in core code, there is no need to track this again in the device drivers. Regards, Joerg
