On Fri, Apr 29, 2022 at 01:06:06PM +0100, Joao Martins wrote: > > TBH I'd be inclined to just enable DBM unconditionally in > > arm_smmu_domain_finalise() if the SMMU supports it. Trying to toggle it > > dynamically (especially on a live domain) seems more trouble that it's > > worth. > > Hmmm, but then it would strip userland/VMM from any sort of control (contrary > to what we can do on the CPU/KVM side). e.g. the first time you do > GET_DIRTY_IOVA it would return all dirtied IOVAs since the beginning > of guest time, as opposed to those only after you enabled dirty-tracking. It just means that on SMMU the start tracking op clears all the dirty bits. I also suppose you'd also want to install the IOPTEs as dirty to avoid a performance regression writing out new dirties for cases where we don't dirty track? And then the start tracking op will switch this so map creates non-dirty IOPTEs? Jason
