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

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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>
This commit is contained in:
George G. Davis 2009-04-01 20:27:18 +01:00 committed by Russell King
parent fe68e68f6a
commit f2255be812
3 changed files with 35 additions and 6 deletions
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23
arch/arm/vfp/entry.S
View file

@ -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

12
arch/arm/vfp/vfphw.S
View file

@ -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:

6
arch/arm/vfp/vfpmodule.c
View file

@ -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)