On Fri, Nov 13, 2020 at 09:37:05AM +0000, Will Deacon wrote: > The aim of this series is to allow 32-bit ARM applications to run on > arm64 SoCs where not all of the CPUs support the 32-bit instruction set. > > There are some major changes in v3: > > * Add some scheduler hooks for restricting a task's affinity mask > * Implement these hooks for arm64 so that we can avoid 32-bit tasks > running on 64-bit-only cores > * Restrict affinity mask of 32-bit tasks on execve() > * Prevent hot-unplug of all 32-bit CPUs if we have a mismatched system > * Ensure 32-bit EL0 cpumask is zero-initialised (oops) > > It's worth mentioning that this approach goes directly against my > initial proposal for punting the affinity management to userspace, > because it turns out that doesn't really work. There are cases where the > kernel has to muck with the affinity mask explicitly, such as execve(), > CPU hotplug and cpuset balancing. Ensuring that these don't lead to > random SIGKILLs as far as userspace is concerned means avoiding any Mooo, I thought we were okay with that... Use does stupid, user gets SIGKIL. What changed? > 64-bit-only CPUs appearing in the affinity mask for a 32-bit task, at > which point it's easier just to handle everything in the kernel anyway.
