4 files changed, 18 insertions, 37 deletions

diff --git a/Documentation/powerpc/transactional_memory.txt b/Documentation/powerpc/transactional_memory.txt
index ba0a2a4a54ba..ded69794a5c0 100644
--- a/Documentation/powerpc/transactional_memory.txt
+++ b/Documentation/powerpc/transactional_memory.txt
@@ -74,23 +74,22 @@ Causes of transaction aborts
 Syscalls
 ========
 
-Syscalls made from within an active transaction will not be performed and the
-transaction will be doomed by the kernel with the failure code TM_CAUSE_SYSCALL
-| TM_CAUSE_PERSISTENT.
+Performing syscalls from within transaction is not recommended, and can lead
+to unpredictable results.
 
-Syscalls made from within a suspended transaction are performed as normal and
-the transaction is not explicitly doomed by the kernel.  However, what the
-kernel does to perform the syscall may result in the transaction being doomed
-by the hardware.  The syscall is performed in suspended mode so any side
-effects will be persistent, independent of transaction success or failure.  No
-guarantees are provided by the kernel about which syscalls will affect
-transaction success.
+Syscalls do not by design abort transactions, but beware: The kernel code will
+not be running in transactional state.  The effect of syscalls will always
+remain visible, but depending on the call they may abort your transaction as a
+side-effect, read soon-to-be-aborted transactional data that should not remain
+invisible, etc.  If you constantly retry a transaction that constantly aborts
+itself by calling a syscall, you'll have a livelock & make no progress.
 
-Care must be taken when relying on syscalls to abort during active transactions
-if the calls are made via a library.  Libraries may cache values (which may
-give the appearance of success) or perform operations that cause transaction
-failure before entering the kernel (which may produce different failure codes).
-Examples are glibc's getpid() and lazy symbol resolution.
+Simple syscalls (e.g. sigprocmask()) "could" be OK.  Even things like write()
+from, say, printf() should be OK as long as the kernel does not access any
+memory that was accessed transactionally.
+
+Consider any syscalls that happen to work as debug-only -- not recommended for
+production use.  Best to queue them up till after the transaction is over.
 
 
 Signals
@@ -177,7 +176,8 @@ kernel aborted a transaction:
  TM_CAUSE_RESCHED       Thread was rescheduled.
  TM_CAUSE_TLBI          Software TLB invalid.
  TM_CAUSE_FAC_UNAV      FP/VEC/VSX unavailable trap.
- TM_CAUSE_SYSCALL       Syscall from active transaction.
+ TM_CAUSE_SYSCALL       Currently unused; future syscalls that must abort
+                        transactions for consistency will use this.
  TM_CAUSE_SIGNAL        Signal delivered.
  TM_CAUSE_MISC          Currently unused.
  TM_CAUSE_ALIGNMENT     Alignment fault.
diff --git a/arch/powerpc/include/uapi/asm/tm.h b/arch/powerpc/include/uapi/asm/tm.h
index 5047659815a5..5d836b7c1176 100644
--- a/arch/powerpc/include/uapi/asm/tm.h
+++ b/arch/powerpc/include/uapi/asm/tm.h
@@ -11,7 +11,7 @@
 #define TM_CAUSE_RESCHED        0xde
 #define TM_CAUSE_TLBI           0xdc
 #define TM_CAUSE_FAC_UNAV       0xda
-#define TM_CAUSE_SYSCALL        0xd8
+#define TM_CAUSE_SYSCALL        0xd8  /* future use */
 #define TM_CAUSE_MISC           0xd6  /* future use */
 #define TM_CAUSE_SIGNAL         0xd4
 #define TM_CAUSE_ALIGNMENT      0xd2
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 8ca9434c40e6..afbc20019c2e 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -34,7 +34,6 @@
 #include <asm/ftrace.h>
 #include <asm/hw_irq.h>
 #include <asm/context_tracking.h>
-#include <asm/tm.h>
 
 /*
  * System calls.
@@ -146,24 +145,6 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
         andi.   r11,r10,_TIF_SYSCALL_DOTRACE
         bne     syscall_dotrace
 .Lsyscall_dotrace_cont:
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-BEGIN_FTR_SECTION
-        b       1f
-END_FTR_SECTION_IFCLR(CPU_FTR_TM)
-        extrdi. r11, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
-        beq+    1f
-
-        /* Doom the transaction and don't perform the syscall: */
-        mfmsr   r11
-        li      r12, 1
-        rldimi  r11, r12, MSR_TM_LG, 63-MSR_TM_LG
-        mtmsrd  r11, 0
-        li      r11, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
-        TABORT(R11)
-
-        b       .Lsyscall_exit
-1:
-#endif
         cmpldi  0,r0,NR_syscalls
         bge-    syscall_enosys
 
diff --git a/tools/testing/selftests/powerpc/tm/Makefile b/tools/testing/selftests/powerpc/tm/Makefile
index 1b616fa79e93..6bff955e1d55 100644
--- a/tools/testing/selftests/powerpc/tm/Makefile
+++ b/tools/testing/selftests/powerpc/tm/Makefile
@@ -1,4 +1,4 @@
-TEST_PROGS := tm-resched-dscr tm-syscall
+TEST_PROGS := tm-resched-dscr
 
 all: $(TEST_PROGS)