arm64: close a race in SVE register managementHEADmain

While testing an unrelated pmap change, D58708, that dramatically
reduces the number of TLBI instructions performed, and likely the
timing of unrelated events, I started seeing "Storing an invalid VFP
state" panics in vfp_save_state_common().  However, the origin of this
panic is elsewhere, in the else branch of sve_restore_state().
Specifically, my pmap change seems to have increased the likelihood that
the thread executing the else branch would be preempted by another
thread between the critical_exit() inside the else branch's call to
vfp_restore_state_common() and its own call to critical_enter().  Prior
to expanding the scope of the else branch's critical section, the MPASS
added by this change would fire, catching the problem at its source,
rather than later in vfp_save_state_common().

Assisted-by:	Claude Code (Opus 5)
Reviewed by:	kib, markj
MFC after: 	1 week
Differential Revision:	https://reviews.freebsd.org/D58723

0 files changed, 0 insertions, 0 deletions