[PATCH 1/3] powerpc: Avoid load hit store in __giveup_fpu() and __giveup_altivec()

[Anton Blanchard]

From: Anton Blanchard <anton at samba.org>

In both __giveup_fpu() and __giveup_altivec() we make two modifications
to tsk->thread.regs->msr. gcc decides to do a read/modify/write of
each change, so we end up with a load hit store:

        ld      r9,264(r10)
        rldicl  r9,r9,50,1
        rotldi  r9,r9,14
        std     r9,264(r10)
...
        ld      r9,264(r10)
        rldicl  r9,r9,40,1
        rotldi  r9,r9,24
        std     r9,264(r10)

Fix this by using a temporary.

Signed-off-by: Anton Blanchard <anton at samba.org>
---
 arch/powerpc/kernel/process.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index e2f12cb..7da1f92 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -139,12 +139,16 @@ EXPORT_SYMBOL(__msr_check_and_clear);
 #ifdef CONFIG_PPC_FPU
 void __giveup_fpu(struct task_struct *tsk)
 {
+	u64 msr;
+
 	save_fpu(tsk);
-	tsk->thread.regs->msr &= ~MSR_FP;
+	msr = tsk->thread.regs->msr;
+	msr &= ~MSR_FP;
 #ifdef CONFIG_VSX
 	if (cpu_has_feature(CPU_FTR_VSX))
-		tsk->thread.regs->msr &= ~MSR_VSX;
+		msr &= ~MSR_VSX;
 #endif
+	tsk->thread.regs->msr = msr;
 }
 
 void giveup_fpu(struct task_struct *tsk)
@@ -219,12 +223,16 @@ static int restore_fp(struct task_struct *tsk) { return 0; }
 
 static void __giveup_altivec(struct task_struct *tsk)
 {
+	u64 msr;
+
 	save_altivec(tsk);
-	tsk->thread.regs->msr &= ~MSR_VEC;
+	msr = tsk->thread.regs->msr;
+	msr &= ~MSR_VEC;
 #ifdef CONFIG_VSX
 	if (cpu_has_feature(CPU_FTR_VSX))
-		tsk->thread.regs->msr &= ~MSR_VSX;
+		msr &= ~MSR_VSX;
 #endif
+	tsk->thread.regs->msr = msr;
 }
 
 void giveup_altivec(struct task_struct *tsk)
-- 
2.7.4