On Sat, Jan 29, 2022 at 12:46:59PM +0100, Greg Kroah-Hartman wrote:
On Fri, Jan 28, 2022 at 06:53:01PM +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
5.9.x is long end-of-life, did you mean to do this for 5.10.y?
Ah, true, not sure how I ended up checking out the 5.9 stable branch (maybe I had 4.9 in mind for an unrelated thing and just thought of something .9).
I'll send you a backport to 5.10.