x86/speculation: Add __update_spec_ctrl() helper

[ Upstream commit e3e3bab1 ]

Add a new __update_spec_ctrl() helper which is a variant of
update_spec_ctrl() that can be used in a noinstr function.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20230727184600.26768-2-longman@redhat.com


Stable-dep-of: c157d351 ("intel_idle: Handle older CPUs, which stop the TSC in deeper C states, correctly")
Signed-off-by: Sasha Levin <sashal@kernel.org>