On Sun, Oct 20, 2024 at 03:59:25PM -0700, Linus Torvalds wrote: > On Sun, 20 Oct 2024 at 15:44, Josh Poimboeuf <jpoim...@kernel.org> wrote: > > > > Anyway, I'd really like to make forward progress on getting rid of the > > LFENCEs in copy_from_user() and __get_user(), so until if/when we hear > > back from both vendors, how about we avoid noncanonical exceptions > > altogether (along with the edge cases mentioned above) and do something > > like the below? > > That doesn't work for LAM at _all_. > > So at a minimum, you need to then say "for LAM enabled CPU's we do the > 'shift sign bit' trick". > > Hopefully any LAM-capable CPU doesn't have this issue?
LAM brings own speculation issues[1] that is going to be addressed by LASS[2]. There was a patch[3] to disable LAM until LASS is landed, but it never got applied for some reason. [1] https://download.vusec.net/papers/slam_sp24.pdf [2] https://lore.kernel.org/all/20240710160655.3402786-1-alexander.shish...@linux.intel.com [3] https://lore.kernel.org/all/5373262886f2783f054256babdf5a98545dc986b.1706068222.git.pawan.kumar.gu...@linux.intel.com -- Kiryl Shutsemau / Kirill A. Shutemov
