On Sun, 27 Mar 2022 17:30:01 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, Mar 27, 2022 at 4:52 PM Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > > I have no intention of pursuing this. When fixing the information leak, > > I happened to realize, that a somewhat similar situation can emerge when > > mappings are reused. It seemed like an easy fix, so I asked the swiotlb > > maintainers, and they agreed. It ain't my field of expertise, and the > > drivers I'm interested in don't need this functionality. > > Ok. > > That said, I think you are putting yourself down when you said in an > earlier email that you aren't veryt knowledgeable in this area. > > I think the fact that you *did* think of this other similar situation > is actually very interesting, and it's something people probably > _haven't_ been thinking about. Thank you! > > So I think your first commit fixes the straightforward and common case > where you do that "map / partial dma / unmap" case. > > And that straightforward case is probably all that the disk IO case > ever really triggers, which is presumably why those "drivers I'm > interested in don't need this functionality" don't need anything else? > I agree. > And yes, your second commit didn't work, but hey, whatever. The whole > "multiple operations on the same double buffering allocation" > situation is something I don't think people have necessarily thought > about enough. > > And by that I don't mean you. I mean very much the whole history of > our dma mapping code. > I agree. We are in the process of catching up! :) My idea was to aid a process, as a relatively naive pair of eyes: somebody didn't read any data sheets describing non-cache-coherent DMA, and never programmed a DMA. It is a fairly common problem, that for the very knowledgeable certain things seem obvious, self-explanatory or trivial, but for the less knowledgeable the are not. And knowledge can create bias. > I then get opinionated and probably too forceful, but please don't > take it as being about you - it's about just my frustration with that > code - and if it comes off too negative then please accept my > apologies. I have to admit, I did feel a little uncomfortable, and I did look for an exit strategy. I do believe, that people in your position do have to occasionally get forceful, and even abrasive to maintain efficiency. I try to not ignore the social aspect of things, but I do get carried away occasionally. Your last especially paragraph is very encouraging and welcome. Thank you! Regards, Halil [..]
