> From: Zhao, Yan Y <yan.y.zhao@xxxxxxxxx> > Sent: Thursday, May 16, 2024 10:33 AM > > On Wed, May 15, 2024 at 05:43:04PM -0300, Jason Gunthorpe wrote: > > On Wed, May 15, 2024 at 03:06:36PM +0800, Yan Zhao wrote: > > > > > > So it has to be calculated on closer to a page by page basis (really a > > > > span by span basis) if flushing of that span is needed based on where > > > > the pages came from. Only pages that came from a hwpt that is > > > > non-coherent can skip the flushing. > > > Is area by area basis also good? > > > Isn't an area either not mapped to any domain or mapped into all > domains? > > > > Yes, this is what the span iterator turns into in the background, it > > goes area by area to cover things. > > > > > But, yes, considering the limited number of non-coherent domains, it > appears > > > more robust and clean to always flush for non-coherent domain in > > > iopt_area_fill_domain(). > > > It eliminates the need to decide whether to retain the area flag during a > split. > > > > And flush for pin user pages, so you basically always flush because > > you can't tell where the pages came from. > As a summary, do you think it's good to flush in below way? > > 1. in iopt_area_fill_domains(), flush before mapping a page into domains > when > iopt->noncoherent_domain_cnt > 0, no matter where the page is from. > Record cache_flush_required in pages for unpin. > 2. in iopt_area_fill_domain(), pass in hwpt to check domain non-coherency. > flush before mapping a page into a non-coherent domain, no matter where > the > page is from. > Record cache_flush_required in pages for unpin. > 3. in batch_unpin(), flush if pages->cache_flush_required before > unpin_user_pages. so above suggests a sequence similar to vfio_type1 does?
