• Dave Martin's avatar
    arm64: neon: Remove support for nested or hardirq kernel-mode NEON · cb84d11e
    Dave Martin authored
    Support for kernel-mode NEON to be nested and/or used in hardirq
    context adds significant complexity, and the benefits may be
    marginal.  In practice, kernel-mode NEON is not used in hardirq
    context, and is rarely used in softirq context (by certain mac80211
    This patch implements an arm64 may_use_simd() function to allow
    clients to check whether kernel-mode NEON is usable in the current
    context, and simplifies kernel_neon_{begin,end}() to handle only
    saving of the task FPSIMD state (if any).  Without nesting, there
    is no other state to save.
    The partial fpsimd save/restore functions become redundant as a
    result of these changes, so they are removed too.
    The save/restore model is changed to operate directly on
    task_struct without additional percpu storage.  This simplifies the
    code and saves a bit of memory, but means that softirqs must now be
    disabled when manipulating the task fpsimd state from task context:
    correspondingly, preempt_{en,dis}sable() calls are upgraded to
    local_bh_{en,dis}able() as appropriate.  fpsimd_thread_switch()
    already runs with hardirqs disabled and so is already protected
    from softirqs.
    These changes should make it easier to support kernel-mode NEON in
    the presence of the Scalable Vector extension in the future.
    Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
    Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
entry-fpsimd.S 1.08 KB