On Sat, Jan 29, 2022 at 01:38:27PM +0000, Catalin Marinas wrote:
From: D Scott Phillips scott@os.amperecomputing.com
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@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
arch/arm64/kernel/process.c | 39 +++++++++++++++---------------------- 1 file changed, 16 insertions(+), 23 deletions(-)
Thanks, both backports now queued up.
greg k-h