On Thu, Nov 19, 2020 at 05:11:27PM +0100, Peter Zijlstra wrote: > 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? See my other reply, but there are 64-bit apps that execve() a 32-bit payload. I was hoping this could be handling in the C library, but that has no idea about what it's exec'ing beyond the path. Will
