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linux/arch/arm/vfp/vfphw.S
George G. Davis f2255be812 [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>
2009-04-01 22:17:50 +01:00

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/*
* linux/arch/arm/vfp/vfphw.S
*
* Copyright (C) 2004 ARM Limited.
* Written by Deep Blue Solutions Limited.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This code is called from the kernel's undefined instruction trap.
* r9 holds the return address for successful handling.
* lr holds the return address for unrecognised instructions.
* r10 points at the start of the private FP workspace in the thread structure
* sp points to a struct pt_regs (as defined in include/asm/proc/ptrace.h)
*/
#include <asm/thread_info.h>
#include <asm/vfpmacros.h>
#include "../kernel/entry-header.S"
.macro DBGSTR, str
#ifdef DEBUG
stmfd sp!, {r0-r3, ip, lr}
add r0, pc, #4
bl printk
b 1f
.asciz "<7>VFP: \str\n"
.balign 4
1: ldmfd sp!, {r0-r3, ip, lr}
#endif
.endm
.macro DBGSTR1, str, arg
#ifdef DEBUG
stmfd sp!, {r0-r3, ip, lr}
mov r1, \arg
add r0, pc, #4
bl printk
b 1f
.asciz "<7>VFP: \str\n"
.balign 4
1: ldmfd sp!, {r0-r3, ip, lr}
#endif
.endm
.macro DBGSTR3, str, arg1, arg2, arg3
#ifdef DEBUG
stmfd sp!, {r0-r3, ip, lr}
mov r3, \arg3
mov r2, \arg2
mov r1, \arg1
add r0, pc, #4
bl printk
b 1f
.asciz "<7>VFP: \str\n"
.balign 4
1: ldmfd sp!, {r0-r3, ip, lr}
#endif
.endm
@ VFP hardware support entry point.
@
@ r0 = faulted instruction
@ r2 = faulted PC+4
@ r9 = successful return
@ r10 = vfp_state union
@ r11 = CPU number
@ lr = failure return
ENTRY(vfp_support_entry)
DBGSTR3 "instr %08x pc %08x state %p", r0, r2, r10
VFPFMRX r1, FPEXC @ Is the VFP enabled?
DBGSTR1 "fpexc %08x", r1
tst r1, #FPEXC_EN
bne look_for_VFP_exceptions @ VFP is already enabled
DBGSTR1 "enable %x", r10
ldr r3, last_VFP_context_address
orr r1, r1, #FPEXC_EN @ user FPEXC has the enable bit set
ldr r4, [r3, r11, lsl #2] @ last_VFP_context pointer
bic r5, r1, #FPEXC_EX @ make sure exceptions are disabled
cmp r4, r10
beq check_for_exception @ we are returning to the same
@ process, so the registers are
@ still there. In this case, we do
@ not want to drop a pending exception.
VFPFMXR FPEXC, r5 @ enable VFP, disable any pending
@ exceptions, so we can get at the
@ rest of it
#ifndef CONFIG_SMP
@ Save out the current registers to the old thread state
@ No need for SMP since this is not done lazily
DBGSTR1 "save old state %p", r4
cmp r4, #0
beq no_old_VFP_process
VFPFSTMIA r4, r5 @ save the working registers
VFPFMRX r5, FPSCR @ current status
tst r1, #FPEXC_EX @ is there additional state to save?
beq 1f
VFPFMRX r6, FPINST @ FPINST (only if FPEXC.EX is set)
tst r1, #FPEXC_FP2V @ is there an FPINST2 to read?
beq 1f
VFPFMRX r8, FPINST2 @ FPINST2 if needed (and present)
1:
stmia r4, {r1, r5, r6, r8} @ save FPEXC, FPSCR, FPINST, FPINST2
@ and point r4 at the word at the
@ start of the register dump
#endif
no_old_VFP_process:
DBGSTR1 "load state %p", r10
str r10, [r3, r11, lsl #2] @ update the last_VFP_context pointer
@ Load the saved state back into the VFP
VFPFLDMIA r10, r5 @ reload the working registers while
@ FPEXC is in a safe state
ldmia r10, {r1, r5, r6, r8} @ load FPEXC, FPSCR, FPINST, FPINST2
tst r1, #FPEXC_EX @ is there additional state to restore?
beq 1f
VFPFMXR FPINST, r6 @ restore FPINST (only if FPEXC.EX is set)
tst r1, #FPEXC_FP2V @ is there an FPINST2 to write?
beq 1f
VFPFMXR FPINST2, r8 @ FPINST2 if needed (and present)
1:
VFPFMXR FPSCR, r5 @ restore status
check_for_exception:
tst r1, #FPEXC_EX
bne process_exception @ might as well handle the pending
@ exception before retrying branch
@ out before setting an FPEXC that
@ stops us reading stuff
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
look_for_VFP_exceptions:
@ Check for synchronous or asynchronous exception
tst r1, #FPEXC_EX | FPEXC_DEX
bne process_exception
@ On some implementations of the VFP subarch 1, setting FPSCR.IXE
@ causes all the CDP instructions to be bounced synchronously without
@ setting the FPEXC.EX bit
VFPFMRX r5, FPSCR
tst r5, #FPSCR_IXE
bne process_exception
@ Fall into hand on to next handler - appropriate coproc instr
@ 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:
DBGSTR "bounce"
mov r2, sp @ nothing stacked - regdump is at TOS
mov lr, r9 @ setup for a return to the user code.
@ Now call the C code to package up the bounce to the support code
@ r0 holds the trigger instruction
@ r1 holds the FPEXC value
@ r2 pointer to register dump
b VFP_bounce @ we have handled this - the support
@ code will raise an exception if
@ required. If not, the user code will
@ retry the faulted instruction
ENDPROC(vfp_support_entry)
ENTRY(vfp_save_state)
@ Save the current VFP state
@ r0 - save location
@ r1 - FPEXC
DBGSTR1 "save VFP state %p", r0
VFPFSTMIA r0, r2 @ save the working registers
VFPFMRX r2, FPSCR @ current status
tst r1, #FPEXC_EX @ is there additional state to save?
beq 1f
VFPFMRX r3, FPINST @ FPINST (only if FPEXC.EX is set)
tst r1, #FPEXC_FP2V @ is there an FPINST2 to read?
beq 1f
VFPFMRX r12, FPINST2 @ FPINST2 if needed (and present)
1:
stmia r0, {r1, r2, r3, r12} @ save FPEXC, FPSCR, FPINST, FPINST2
mov pc, lr
ENDPROC(vfp_save_state)
last_VFP_context_address:
.word last_VFP_context
ENTRY(vfp_get_float)
add pc, pc, r0, lsl #3
mov r0, r0
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
mrc p10, 0, r0, c\dr, c0, 0 @ fmrs r0, s0
mov pc, lr
mrc p10, 0, r0, c\dr, c0, 4 @ fmrs r0, s1
mov pc, lr
.endr
ENDPROC(vfp_get_float)
ENTRY(vfp_put_float)
add pc, pc, r1, lsl #3
mov r0, r0
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
mcr p10, 0, r0, c\dr, c0, 0 @ fmsr r0, s0
mov pc, lr
mcr p10, 0, r0, c\dr, c0, 4 @ fmsr r0, s1
mov pc, lr
.endr
ENDPROC(vfp_put_float)
ENTRY(vfp_get_double)
add pc, pc, r0, lsl #3
mov r0, r0
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
fmrrd r0, r1, d\dr
mov pc, lr
.endr
#ifdef CONFIG_VFPv3
@ d16 - d31 registers
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
mrrc p11, 3, r0, r1, c\dr @ fmrrd r0, r1, d\dr
mov pc, lr
.endr
#endif
@ virtual register 16 (or 32 if VFPv3) for compare with zero
mov r0, #0
mov r1, #0
mov pc, lr
ENDPROC(vfp_get_double)
ENTRY(vfp_put_double)
add pc, pc, r2, lsl #3
mov r0, r0
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
fmdrr d\dr, r0, r1
mov pc, lr
.endr
#ifdef CONFIG_VFPv3
@ d16 - d31 registers
.irp dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
mcrr p11, 3, r1, r2, c\dr @ fmdrr r1, r2, d\dr
mov pc, lr
.endr
#endif
ENDPROC(vfp_put_double)
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