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    SubjectRe: [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems
    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.

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