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authorMichael Ellerman <mpe@ellerman.id.au>2018-11-29 09:42:24 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2019-02-23 14:31:39 +0300
commite7fda7e569e1776d4dccbcef52d34882b62b0654 (patch)
tree06c73856748dd3aa8a2a82aca4df35c9c8c801f1 /arch/powerpc/kernel
parentfb0b0a73b223fc113e961b1d921322844e9c30d9 (diff)
downloadlinux-e7fda7e569e1776d4dccbcef52d34882b62b0654.tar.xz
powerpc/64s: Remove MSR_RI optimisation in system_call_exit()
Currently in system_call_exit() we have an optimisation where we disable MSR_RI (recoverable interrupt) and MSR_EE (external interrupt enable) in a single mtmsrd instruction. Unfortunately this will no longer work with THREAD_INFO_IN_TASK, because then the load of TI_FLAGS might fault and faulting with MSR_RI clear is treated as an unrecoverable exception which leads to a panic(). So change the code to only clear MSR_EE prior to loading TI_FLAGS, leaving the clear of MSR_RI until later. We have some latitude in where do the clear of MSR_RI. A bit of experimentation has shown that this location gives the least slow down. This still causes a noticeable slow down in our null_syscall performance. On a Power9 DD2.2: Before After Delta Delta % 955 cycles 999 cycles -44 -4.6% On the plus side this does simplify the code somewhat, because we don't have to reenable MSR_RI on the restore_math() or syscall_exit_work() paths which was necessitated previously by the optimisation. Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel')
-rw-r--r--arch/powerpc/kernel/entry_64.S34
1 files changed, 14 insertions, 20 deletions
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index a2c168b395d2..c17c1bed6148 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -236,18 +236,14 @@ system_call_exit:
/*
* Disable interrupts so current_thread_info()->flags can't change,
* and so that we don't get interrupted after loading SRR0/1.
+ *
+ * Leave MSR_RI enabled for now, because with THREAD_INFO_IN_TASK we
+ * could fault on the load of the TI_FLAGS below.
*/
#ifdef CONFIG_PPC_BOOK3E
wrteei 0
#else
- /*
- * For performance reasons we clear RI the same time that we
- * clear EE. We only need to clear RI just before we restore r13
- * below, but batching it with EE saves us one expensive mtmsrd call.
- * We have to be careful to restore RI if we branch anywhere from
- * here (eg syscall_exit_work).
- */
- li r11,0
+ li r11,MSR_RI
mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
@@ -263,15 +259,7 @@ system_call_exit:
bne 3f
#endif
2: addi r3,r1,STACK_FRAME_OVERHEAD
-#ifdef CONFIG_PPC_BOOK3S
- li r10,MSR_RI
- mtmsrd r10,1 /* Restore RI */
-#endif
bl restore_math
-#ifdef CONFIG_PPC_BOOK3S
- li r11,0
- mtmsrd r11,1
-#endif
ld r8,_MSR(r1)
ld r3,RESULT(r1)
li r11,-MAX_ERRNO
@@ -287,6 +275,16 @@ END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
andi. r6,r8,MSR_PR
ld r4,_LINK(r1)
+#ifdef CONFIG_PPC_BOOK3S
+ /*
+ * Clear MSR_RI, MSR_EE is already and remains disabled. We could do
+ * this later, but testing shows that doing it here causes less slow
+ * down than doing it closer to the rfid.
+ */
+ li r11,0
+ mtmsrd r11,1
+#endif
+
beq- 1f
ACCOUNT_CPU_USER_EXIT(r13, r11, r12)
@@ -363,10 +361,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
b .Lsyscall_exit
.Lsyscall_exit_work:
-#ifdef CONFIG_PPC_BOOK3S
- li r10,MSR_RI
- mtmsrd r10,1 /* Restore RI */
-#endif
/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
If TIF_NOERROR is set, just save r3 as it is. */