On Mon, Apr 20, 2020 at 01:44:56PM +0200, Christian König wrote: > Am 20.04.20 um 10:10 schrieb Christoph Hellwig: > > On Mon, Apr 20, 2020 at 09:42:13AM +0200, Jean-Philippe Brucker wrote: > > > Right, I can see the appeal. I still like having a single mmu notifier per > > > mm because it ensures we allocate a single PASID per mm (as required by > > > x86). I suppose one alternative is to maintain a hashtable of mm->pasid, > > > to avoid iterating over all bonds during allocation. > > Given that the PASID is a pretty generic and important concept can > > we just add it directly to the mm_struct and allocate it lazily once > > we first need it? > > Well the problem is that the PASID might as well be device specific. E.g. > some devices use 16bit PASIDs, some 15bit, some other only 12bit. > > So what could (at least in theory) happen is that you need to allocate > different PASIDs for the same process because different devices need one. This directly contradicts the statement from Jean-Philippe above that x86 requires a single PASID per mm_struct. If we may need different PASIDs for different devices and can actually support this just allocating one per [device, mm_struct] would make most sense of me, as it doesn't couple otherwise disjoint state.
