From f2255be8126e86142901c61dd482c1c2a5ffdda7 Mon Sep 17 00:00:00 2001 From: "George G. Davis" Date: Wed, 1 Apr 2009 20:27:18 +0100 Subject: [PATCH] [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 Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/vfp/entry.S | 23 +++++++++++++++++++---- arch/arm/vfp/vfphw.S | 12 ++++++++++++ arch/arm/vfp/vfpmodule.c | 6 ++++-- 3 files changed, 35 insertions(+), 6 deletions(-) diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S index ba592a9e6fb3..a2bed62aec21 100644 --- a/arch/arm/vfp/entry.S +++ b/arch/arm/vfp/entry.S @@ -15,13 +15,16 @@ * r10 = thread_info structure * lr = failure return */ -#include -#include -#include -#include +#include #include +#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 a5a4e57763c3..83c4e384b16d 100644 --- 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 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) -- 2.39.5