linux-kernel - [5/6] powerpc: Disable VSX or current process in giveup

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Date:	Thu, 14 Jan 2010 15:04:53 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Michael Neuling <mikey@...ling.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: [5/6] powerpc: Disable VSX or current process in giveup_fpu/altivec

2.6.27-stable review patch.  If anyone has any objections, please let us know.

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

From: Michael Neuling <mikey@...ling.org>

commit 7e875e9dc8af70d126fa632446e967327ac3fdda upstream.

When we call giveup_fpu, we need to need to turn off VSX for the
current process.  If we don't, on return to userspace it may execute a
VSX instruction before the next FP instruction, and not have its
register state refreshed correctly from the thread_struct.  Ditto for
altivec.

This caused a bug where an unaligned lfs or stfs results in
fix_alignment calling giveup_fpu so it can use the FPRs (in order to
do a single <-> double conversion), and then returning to userspace
with FP off but VSX on.  Then if a VSX instruction is executed, before
another FP instruction, it will proceed without another exception and
hence have the incorrect register state for VSX registers 0-31.

   lfs unaligned   <- alignment exception turns FP off but leaves VSX on

   VSX instruction <- no exception since VSX on, hence we get the
                      wrong VSX register values for VSX registers 0-31,
                      which overlap the FPRs.

Signed-off-by: Michael Neuling <mikey@...ling.org>
Signed-off-by: Paul Mackerras <paulus@...ba.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/powerpc/kernel/fpu.S     |    5 +++++
 arch/powerpc/kernel/misc_64.S |    8 ++++++++
 2 files changed, 13 insertions(+)

--- a/arch/powerpc/kernel/fpu.S
+++ b/arch/powerpc/kernel/fpu.S
@@ -145,6 +145,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX)
 	beq	1f
 	PPC_LL	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
 	li	r3,MSR_FP|MSR_FE0|MSR_FE1
+#ifdef CONFIG_VSX
+BEGIN_FTR_SECTION
+	oris	r3,r3,MSR_VSX@h
+END_FTR_SECTION_IFSET(CPU_FTR_VSX)
+#endif
 	andc	r4,r4,r3		/* disable FP for previous task */
 	PPC_STL	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
 1:
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -493,7 +493,15 @@ _GLOBAL(giveup_altivec)
 	stvx	vr0,r4,r3
 	beq	1f
 	ld	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
+#ifdef CONFIG_VSX
+BEGIN_FTR_SECTION
+	lis	r3,(MSR_VEC|MSR_VSX)@h
+FTR_SECTION_ELSE
+	lis	r3,MSR_VEC@h
+ALT_FTR_SECTION_END_IFSET(CPU_FTR_VSX)
+#else
 	lis	r3,MSR_VEC@h
+#endif
 	andc	r4,r4,r3		/* disable FP for previous task */
 	std	r4,_MSR-STACK_FRAME_OVERHEAD(r5)
 1:


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