On Tue, 2 Jul 2024 10:39:03 -0700 Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > On Tue, Jul 2, 2024 at 10:36 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > On Tue, 2 Jul 2024 13:21:36 +0000 Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > > > > This series has fixups and cleanups for LAM. Most importantly, patch 1 > > > fixes a sycnhronization issue that may cause crashes of userspace > > > applications. This is a resend of v3, rebased on top of v6.10-rc6. > > > > "Crashes of userspace applications" is bad. Yet the patchset has been > > floating about for four months. > > > > It's unclear (to me) how serious this is. Can you please explain how > > common this is, what the userspace application needs to do to trigger > > this, etc? > > I don't think it would be common. The bug only happens on new hardware > supporting LAM, and it happens in a specific scenario where a > userspace task enables LAM while a kthread is using (borrowing) its > mm_struct on another CPU. > > So it is possible but I certainly wouldn't call it common or easily triggerable. But when people run older (or current) kernels on newer hardware, they will hit this. So a backport to cover 82721d8b25d7 ("x86/mm: Handle LAM on context switch") is needed. The series doesn't seem to be getting much traction so I can add it to mm.git's mm-unstable branch for wider testing, but it's clearly an x86 tree thing.