On Saturday, July 25, 2020 12:59 AM, Duncan <1i5t5.duncan@xxxxxxx> wrote: > On Sat, 25 Jul 2020 03:03:52 +0000 > Mazin Rezk mnrzk@xxxxxxxxxxxxxx wrote: > > > > Am 24.07.20 um 19:33 schrieb Kees Cook: > > > > > > > There was a fix to disable the async path for this driver that > > > > worked around the bug too, yes? That seems like a safer and more > > > > focused change that doesn't revert the SLUB defense for all > > > > users, and would actually provide a complete, I think, workaround > > > > That said, I haven't seen the async disabling patch. If you could > > link to it, I'd be glad to test it out and perhaps we can use that > > instead. > > I'm confused. Not to put words in Kees' mouth; /I/ am confused (which > admittedly could well be just because I make no claims to be a > coder and am simply reading the bug and thread, but I'd appreciate some > "unconfusing" anyway). > > My interpretation of the "async disabling" reference was that it was to > comment #30 on the bug: > > https://bugzilla.kernel.org/show_bug.cgi?id=207383#c30 > > ... which (if I'm not confused on this point too) appears to be yours. > There it was stated... > > > > > > > > I've also found that this bug exclusively occurs when commit_work is on > the workqueue. After forcing drm_atomic_helper_commit to run all of the > commits without adding to the workqueue and running the OS, the issue > seems to have disappeared. > <<<< > > Would not forcing all commits to run directly, without placing them on > the workqueue, be "async disabling"? That's what I /thought/ he was > referencing. Oh, I thought he was referring to a different patch. Kees, could I get your confirmation on this? The change I made actually affected all of the DRM code, although this could easily be changed to be specific to amdgpu. (By forcing blocking on amdgpu_dm's non-blocking commit code) That said, I'd still need to test further because I only did test it for a couple of hours then. Although it should work in theory. > > OTOH your base/context swap idea sounds like a possibly "less > disturbance" workaround, if it works, and given the point in the > commit cycle... (But if it's out Sunday it's likely too late to test > and get it in now anyway; if it's another week, tho...) The base/context swap idea should make the use-after-free behave how it did in 5.6. Since the bug doesn't cause an issue in 5.6, it's less of a "less disturbance" workaround and more of a "no disturbance" workaround. Thanks, Mazin Rezk > > ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > > Duncan - No HTML messages please; they are filtered as spam. > "Every nonfree program has a lord, a master -- > and if you use the program, he is your master." Richard Stallman _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
