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- Add a missing memory barrier in the concurrency ID mm switching

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Merge tag 'sched_urgent_for_v6.9_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fix from Borislav Petkov:

 - Add a missing memory barrier in the concurrency ID mm switching

* tag 'sched_urgent_for_v6.9_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched: Add missing memory barrier in switch_mm_cid
This commit is contained in:
Linus Torvalds 2024-04-21 09:39:36 -07:00
commit 3b68086599
3 changed files with 25 additions and 6 deletions
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3
arch/x86/include/asm/barrier.h
View File

@ -79,6 +79,9 @@ do { \
#define __smp_mb__before_atomic() do { } while (0)
#define __smp_mb__after_atomic() do { } while (0)
/* Writing to CR3 provides a full memory barrier in switch_mm(). */
#define smp_mb__after_switch_mm() do { } while (0)
#include <asm-generic/barrier.h>
#endif /* _ASM_X86_BARRIER_H */

8
include/asm-generic/barrier.h
View File

@ -294,5 +294,13 @@ do { \
#define io_stop_wc() do { } while (0)
#endif
/*
* Architectures that guarantee an implicit smp_mb() in switch_mm()
* can override smp_mb__after_switch_mm.
*/
#ifndef smp_mb__after_switch_mm
# define smp_mb__after_switch_mm() smp_mb()
#endif
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */

20
kernel/sched/sched.h
View File

@ -79,6 +79,8 @@
# include <asm/paravirt_api_clock.h>
#endif
#include <asm/barrier.h>
#include "cpupri.h"
#include "cpudeadline.h"
@ -3445,13 +3447,19 @@ static inline void switch_mm_cid(struct rq *rq,
* between rq->curr store and load of {prev,next}->mm->pcpu_cid[cpu].
* Provide it here.
*/
if (!prev->mm) // from kernel
if (!prev->mm) { // from kernel
smp_mb();
/*
* user -> user transition guarantees a memory barrier through
* switch_mm() when current->mm changes. If current->mm is
* unchanged, no barrier is needed.
*/
} else { // from user
/*
* user->user transition relies on an implicit
* memory barrier in switch_mm() when
* current->mm changes. If the architecture
* switch_mm() does not have an implicit memory
* barrier, it is emitted here. If current->mm
* is unchanged, no barrier is needed.
*/
smp_mb__after_switch_mm();
}
}
if (prev->mm_cid_active) {
mm_cid_snapshot_time(rq, prev->mm);