Commit 6ce89512 authored by Mark Rutland's avatar Mark Rutland Committed by Thomas Gleixner
Browse files

entry: Snapshot thread flags 



Some thread flags can be set remotely, and so even when IRQs are disabled,
the flags can change under our feet. Generally this is unlikely to cause a
problem in practice, but it is somewhat unsound, and KCSAN will
legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20211129130653.2037928-3-mark.rutland@arm.com
parent dca99fb6

include/linux/entry-kvm.h

+1 −1
Original line number Diff line number Diff line
@@ -75,7 +75,7 @@ static inline void xfer_to_guest_mode_prepare(void) 
 */

static inline bool __xfer_to_guest_mode_work_pending(void)

{

	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);

	unsigned long ti_work = read_thread_flags();



	return !!(ti_work & XFER_TO_GUEST_MODE_WORK);

}

kernel/entry/common.c

+2 −2
Original line number Diff line number Diff line
@@ -187,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, 
		/* Check if any of the above work has queued a deferred wakeup */

		tick_nohz_user_enter_prepare();



		ti_work = READ_ONCE(current_thread_info()->flags);

		ti_work = read_thread_flags();

	}



	/* Return the latest work state for arch_exit_to_user_mode() */
@@ -196,7 +196,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, 


static void exit_to_user_mode_prepare(struct pt_regs *regs)

{

	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);

	unsigned long ti_work = read_thread_flags();



	lockdep_assert_irqs_disabled();

kernel/entry/kvm.c

+2 −2
Original line number Diff line number Diff line
@@ -26,7 +26,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) 
		if (ret)

			return ret;



		ti_work = READ_ONCE(current_thread_info()->flags);

		ti_work = read_thread_flags();

	} while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched());

	return 0;

}
@@ -43,7 +43,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu) 
	 * disabled in the inner loop before going into guest mode. No need

	 * to disable interrupts here.

	 */

	ti_work = READ_ONCE(current_thread_info()->flags);

	ti_work = read_thread_flags();

	if (!(ti_work & XFER_TO_GUEST_MODE_WORK))

		return 0;