linux-kernel - [PATCH 4.5 018/124] powerpc/process: Fix altivec SPR not being saved

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Message-Id: <20160418022616.676033161@linuxfoundation.org>
Date:	Mon, 18 Apr 2016 11:28:10 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Oliver OHalloran <oohall@...il.com>,
	Anton Blanchard <anton@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.5 018/124] powerpc/process: Fix altivec SPR not being saved

4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oliver O'Halloran <oohall@...il.com>

commit 01d7c2a2de47890934faba91a71d183795e4348d upstream.

In save_sprs() in process.c contains the following test:

	if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC)))
		t->vrsave = mfspr(SPRN_VRSAVE);

CPU feature with the mask 0x1 is CPU_FTR_COHERENT_ICACHE so the test
is equivilent to:

	if (cpu_has_feature(CPU_FTR_ALTIVEC) &&
		cpu_has_feature(CPU_FTR_COHERENT_ICACHE))

On CPUs without support for both (i.e G5) this results in vrsave not
being saved between context switches. The vector register save/restore
code doesn't use VRSAVE to determine which registers to save/restore,
but the value of VRSAVE is used to determine if altivec is being used
in several code paths.

Fixes: 152d523e6307 ("powerpc: Create context switch helpers save_sprs() and restore_sprs()")
Signed-off-by: Oliver O'Halloran <oohall@...il.com>
Signed-off-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kernel/process.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -854,7 +854,7 @@ void restore_tm_state(struct pt_regs *re
 static inline void save_sprs(struct thread_struct *t)
 {
 #ifdef CONFIG_ALTIVEC
-	if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC)))
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
 		t->vrsave = mfspr(SPRN_VRSAVE);
 #endif
 #ifdef CONFIG_PPC_BOOK3S_64