[ARM] 5440/1: Fix VFP state corruption due to preemption during VFP exceptions

We've observed that ARM VFP state can be corrupted during VFP exception
handling when PREEMPT is enabled.  The exact conditions are difficult
to reproduce but appear to occur during VFP exception handling when a
task causes a VFP exception which is handled via VFP_bounce and is then
preempted by yet another task which in turn causes yet another VFP
exception.  Since the VFP_bounce code is not preempt safe, VFP state then
becomes corrupt.  In order to prevent preemption from occuring while
handling a VFP exception, this patch disables preemption while handling
VFP exceptions.

Signed-off-by: George G. Davis <gdavis@mvista.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 75457b30d813..01599c4ef726 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -266,7 +266,7 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
                  * on VFP subarch 1.
                  */
                  vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs);
-                 return;
+                goto exit;
         }
 
         /*
@@ -297,7 +297,7 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
          * the FPEXC.FP2V bit is valid only if FPEXC.EX is 1.
          */
         if (fpexc ^ (FPEXC_EX | FPEXC_FP2V))
-                return;
+                goto exit;
 
         /*
          * The barrier() here prevents fpinst2 being read
@@ -310,6 +310,8 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
         exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs);
         if (exceptions)
                 vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
+ exit:
+        preempt_enable();
 }
 
 static void vfp_enable(void *unused)