powerpc: Improve 64-bit syscall entry/exit

We unconditionally hard enable interrupts. This is unnecessary as
syscalls are expected to always be called with interrupts enabled.

While at it, we add a WARN_ON if that is not the case and
CONFIG_TRACE_IRQFLAGS is enabled (we don't want to add overhead
to the fast path when this is not set though).

Thus let's remove the enabling (and associated irq tracing) from
the syscall entry path. Also on Book3S, replace a few mfmsr
instructions with loads of PACAMSR from the PACA, which should be
faster & schedule better.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 23 insertions, 20 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 0c3764ba8d49..cc030b73174b 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -115,28 +115,33 @@ BEGIN_FW_FTR_SECTION
 END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING && CONFIG_PPC_SPLPAR */
 
-#ifdef CONFIG_TRACE_IRQFLAGS
-        bl      .trace_hardirqs_on
-        REST_GPR(0,r1)
-        REST_4GPRS(3,r1)
-        REST_2GPRS(7,r1)
-        addi    r9,r1,STACK_FRAME_OVERHEAD
-        ld      r12,_MSR(r1)
-#endif /* CONFIG_TRACE_IRQFLAGS */
-        li      r10,1
-        stb     r10,PACASOFTIRQEN(r13)
-        stb     r10,PACAHARDIRQEN(r13)
-        std     r10,SOFTE(r1)
+        /*
+         * A syscall should always be called with interrupts enabled
+         * so we just unconditionally hard-enable here. When some kind
+         * of irq tracing is used, we additionally check that condition
+         * is correct
+         */
+#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_BUG)
+        lbz     r10,PACASOFTIRQEN(r13)
+        xori    r10,r10,1
+1:      tdnei   r10,0
+        EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING
+#endif
 
-        /* Hard enable interrupts */
 #ifdef CONFIG_PPC_BOOK3E
         wrteei  1
 #else
-        mfmsr   r11
+        ld      r11,PACAKMSR(r13)
         ori     r11,r11,MSR_EE
         mtmsrd  r11,1
 #endif /* CONFIG_PPC_BOOK3E */
 
+        /* We do need to set SOFTE in the stack frame or the return
+         * from interrupt will be painful
+         */
+        li      r10,1
+        std     r10,SOFTE(r1)
+
 #ifdef SHOW_SYSCALLS
         bl      .do_show_syscall
         REST_GPR(0,r1)
@@ -187,16 +192,14 @@ syscall_exit:
         andi.   r10,r8,MSR_RI
         beq-    unrecov_restore
 #endif
-
-        /* Disable interrupts so current_thread_info()->flags can't change,
+        /*
+         * Disable interrupts so current_thread_info()->flags can't change,
          * and so that we don't get interrupted after loading SRR0/1.
          */
 #ifdef CONFIG_PPC_BOOK3E
         wrteei  0
 #else
-        mfmsr   r10
-        rldicl  r10,r10,48,1
-        rotldi  r10,r10,16
+        ld      r10,PACAKMSR(r13)
         mtmsrd  r10,1
 #endif /* CONFIG_PPC_BOOK3E */
 
@@ -308,7 +311,7 @@ syscall_exit_work:
 #ifdef CONFIG_PPC_BOOK3E
         wrteei  1
 #else
-        mfmsr   r10
+        ld      r10,PACAKMSR(r13)
         ori     r10,r10,MSR_EE
         mtmsrd  r10,1
 #endif /* CONFIG_PPC_BOOK3E */