[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>

diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index ba592a9..a2bed62 100644 (file)
--- a/arch/arm/vfp/entry.S
+++ b/arch/arm/vfp/entry.S
@@ -15,13 +15,16 @@
  *  r10 = thread_info structure
  *  lr  = failure return
  */
-#include <linux/linkage.h>
-#include <linux/init.h>
-#include <asm/asm-offsets.h>
-#include <asm/assembler.h>
+#include <asm/thread_info.h>
 #include <asm/vfpmacros.h>
+#include "../kernel/entry-header.S"
 
 ENTRY(do_vfp)
+#ifdef CONFIG_PREEMPT
+       ldr     r4, [r10, #TI_PREEMPT]  @ get preempt count
+       add     r11, r4, #1             @ increment it
+       str     r11, [r10, #TI_PREEMPT]
+#endif
        enable_irq
        ldr     r4, .LCvfp
        ldr     r11, [r10, #TI_CPU]     @ CPU number
@@ -30,6 +33,12 @@ ENTRY(do_vfp)
 ENDPROC(do_vfp)
 
 ENTRY(vfp_null_entry)
+#ifdef CONFIG_PREEMPT
+       get_thread_info r10
+       ldr     r4, [r10, #TI_PREEMPT]  @ get preempt count
+       sub     r11, r4, #1             @ decrement it
+       str     r11, [r10, #TI_PREEMPT]
+#endif
        mov     pc, lr
 ENDPROC(vfp_null_entry)
 
@@ -41,6 +50,12 @@ ENDPROC(vfp_null_entry)
 
        __INIT
 ENTRY(vfp_testing_entry)
+#ifdef CONFIG_PREEMPT
+       get_thread_info r10
+       ldr     r4, [r10, #TI_PREEMPT]  @ get preempt count
+       sub     r11, r4, #1             @ decrement it
+       str     r11, [r10, #TI_PREEMPT]
+#endif
        ldr     r0, VFP_arch_address
        str     r5, [r0]                @ known non-zero value
        mov     pc, r9                  @ we have handled the fault

diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index a5a4e57..83c4e38 100644 (file)
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -137,6 +137,12 @@ check_for_exception:
        VFPFMXR FPEXC, r1               @ restore FPEXC last
        sub     r2, r2, #4
        str     r2, [sp, #S_PC]         @ retry the instruction
+#ifdef CONFIG_PREEMPT
+       get_thread_info r10
+       ldr     r4, [r10, #TI_PREEMPT]  @ get preempt count
+       sub     r11, r4, #1             @ decrement it
+       str     r11, [r10, #TI_PREEMPT]
+#endif
        mov     pc, r9                  @ we think we have handled things
 
 
@@ -155,6 +161,12 @@ look_for_VFP_exceptions:
        @ not recognised by VFP
 
        DBGSTR  "not VFP"
+#ifdef CONFIG_PREEMPT
+       get_thread_info r10
+       ldr     r4, [r10, #TI_PREEMPT]  @ get preempt count
+       sub     r11, r4, #1             @ decrement it
+       str     r11, [r10, #TI_PREEMPT]
+#endif
        mov     pc, lr
 
 process_exception:

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 75457b3..01599c4 100644 (file)
--- 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)