summaryrefslogtreecommitdiff
path: root/arch/s390/include/asm/thread_info.h
diff options
context:
space:
mode:
authorMartin Schwidefsky <schwidefsky@de.ibm.com>2012-09-10 15:00:09 +0400
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2014-02-21 11:50:18 +0400
commit53e857f30867918b3618d8e18902e63291946ef4 (patch)
tree53b7875848deb77a0012aaa04169d6d041b52cf1 /arch/s390/include/asm/thread_info.h
parenta53efe5ff88d0283bae8a2c2fa066d0fff31dc91 (diff)
downloadlinux-53e857f30867918b3618d8e18902e63291946ef4.tar.xz
s390/mm,tlb: race of lazy TLB flush vs. recreation of TLB entries
Git commit 050eef364ad70059 "[S390] fix tlb flushing vs. concurrent /proc accesses" introduced the attach counter to avoid using the mm_users value to decide between IPTE for every PTE and lazy TLB flushing with IDTE. That fixed the problem with mm_users but it introduced another subtle race, fortunately one that is very hard to hit. The background is the requirement of the architecture that a valid PTE may not be changed while it can be used concurrently by another cpu. The decision between IPTE and lazy TLB flushing needs to be done while the PTE is still valid. Now if the virtual cpu is temporarily stopped after the decision to use lazy TLB flushing but before the invalid bit of the PTE has been set, another cpu can attach the mm, find that flush_mm is set, do the IDTE, return to userspace, and recreate a TLB that uses the PTE in question. When the first, stopped cpu continues it will change the PTE while it is attached on another cpu. The first cpu will do another IDTE shortly after the modification of the PTE which makes the race window quite short. To fix this race the CPU that wants to attach the address space of a user space thread needs to wait for the end of the PTE modification. The number of concurrent TLB flushers for an mm is tracked in the upper 16 bits of the attach_count and finish_arch_post_lock_switch is used to wait for the end of the flush operation if required. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/include/asm/thread_info.h')
-rw-r--r--arch/s390/include/asm/thread_info.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 10e0fcd3633d..d2e53d667a92 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -81,6 +81,7 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_NOTIFY_RESUME 1 /* callback before returning to user */
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
+#define TIF_TLB_WAIT 4 /* wait for TLB flush completion */
#define TIF_PER_TRAP 6 /* deliver sigtrap on return to user */
#define TIF_MCCK_PENDING 7 /* machine check handling is pending */
#define TIF_SYSCALL_TRACE 8 /* syscall trace active */
@@ -96,6 +97,7 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
+#define _TIF_TLB_WAIT (1<<TIF_TLB_WAIT)
#define _TIF_PER_TRAP (1<<TIF_PER_TRAP)
#define _TIF_MCCK_PENDING (1<<TIF_MCCK_PENDING)
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)