On Sat, Jan 29, 2022 at 01:38:27PM +0000, Catalin Marinas wrote:
> From: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
>
> commit 38e0257e0e6f4fef2aa2966b089b56a8b1cfb75c upstream.
>
> The erratum 1418040 workaround enables CNTVCT_EL1 access trapping in EL0
> when executing compat threads. The workaround is applied when switching
> between tasks, but the need for the workaround could also change at an
> exec(), when a non-compat task execs a compat binary or vice versa. Apply
> the workaround in arch_setup_new_exec().
>
> This leaves a small window of time between SET_PERSONALITY and
> arch_setup_new_exec where preemption could occur and confuse the old
> workaround logic that compares TIF_32BIT between prev and next. Instead, we
> can just read cntkctl to make sure it's in the state that the next task
> needs. I measured cntkctl read time to be about the same as a mov from a
> general-purpose register on N1. Update the workaround logic to examine the
> current value of cntkctl instead of the previous task's compat state.
>
> Fixes: d49f7d7376d0 ("arm64: Move handling of erratum 1418040 into C code")
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.9.x
> Signed-off-by: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20211220234114.3926-1-scott@xxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
> arch/arm64/kernel/process.c | 39 +++++++++++++++----------------------
> 1 file changed, 16 insertions(+), 23 deletions(-)
Thanks, both backports now queued up.
greg k-h
