arm64: errata: Fix exec handling in erratum 1418040 workaround
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: d49f7d73 ("arm64: Move handling of erratum 1418040 into C code") Cc: <stable@vger.kernel.org> # 5.9.x Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com> Reviewed-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20211220234114.3926-1-scott@os.amperecomputing.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Please register or sign in to comment