Commit f2255be8 authored by George G. Davis's avatar George G. Davis Committed by Russell King
Browse files

[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: default avatarGeorge G. Davis <gdavis@mvista.com>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent fe68e68f

arch/arm/vfp/entry.S

+19 −4
Original line number Diff line number Diff line
@@ -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

arch/arm/vfp/vfphw.S

+12 −0
Original line number Diff line number Diff line
@@ -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:

arch/arm/vfp/vfpmodule.c

+4 −2
Original line number Diff line number Diff line
@@ -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)

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