powerpc: Replace mfmsr instructions with load from PACA kernel_msr field

On 64-bit, the mfmsr instruction can be quite slow, slower
than loading a field from the cache-hot PACA, which happens
to already contain the value we want in most cases.

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

1 files changed, 5 insertions, 9 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index cc030b73174b..c513beb78b3b 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -557,10 +557,8 @@ _GLOBAL(ret_from_except_lite)
 #ifdef CONFIG_PPC_BOOK3E
         wrteei  0
 #else
-        mfmsr   r10             /* Get current interrupt state */
-        rldicl  r9,r10,48,1     /* clear MSR_EE */
-        rotldi  r9,r9,16
-        mtmsrd  r9,1            /* Update machine state */
+        ld      r10,PACAKMSR(r13) /* Get kernel MSR without EE */
+        mtmsrd  r10,1             /* Update machine state */
 #endif /* CONFIG_PPC_BOOK3E */
 
 #ifdef CONFIG_PREEMPT
@@ -625,8 +623,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
          * userspace and we take an exception after restoring r13,
          * we end up corrupting the userspace r13 value.
          */
-        mfmsr   r4
-        andc    r4,r4,r0        /* r0 contains MSR_RI here */
+        ld      r4,PACAKMSR(r13) /* Get kernel MSR without EE */
+        andc    r4,r4,r0         /* r0 contains MSR_RI here */
         mtmsrd  r4,1
 
         /*
@@ -686,9 +684,7 @@ do_work:
 #ifdef CONFIG_PPC_BOOK3E
         wrteei  0
 #else
-        mfmsr   r10
-        rldicl  r10,r10,48,1
-        rotldi  r10,r10,16
+        ld      r10,PACAKMSR(r13) /* Get kernel MSR without EE */
         mtmsrd  r10,1
 #endif /* CONFIG_PPC_BOOK3E */
         li      r0,0