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linux/arch/xtensa/kernel/vectors.S
Max Filippov 99d5040ebc xtensa: keep a3 and excsave1 on entry to exception handlers 
Based on the SMP patch by Joe Taylor and subsequent fixes.
Preserve exception table pointer (normally stored in excsave1 SR) as it
cannot be easily restored in SMP environment.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
2013-09-06 09:47:41 -07:00

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19 KiB
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/*
* arch/xtensa/kernel/vectors.S
*
* This file contains all exception vectors (user, kernel, and double),
* as well as the window vectors (overflow and underflow), and the debug
* vector. These are the primary vectors executed by the processor if an
* exception occurs.
*
* This file is subject to the terms and conditions of the GNU General
* Public License. See the file "COPYING" in the main directory of
* this archive for more details.
*
* Copyright (C) 2005 - 2008 Tensilica, Inc.
*
* Chris Zankel <chris@zankel.net>
*
*/
/*
* We use a two-level table approach. The user and kernel exception vectors
* use a first-level dispatch table to dispatch the exception to a registered
* fast handler or the default handler, if no fast handler was registered.
* The default handler sets up a C-stack and dispatches the exception to a
* registerd C handler in the second-level dispatch table.
*
* Fast handler entry condition:
*
* a0: trashed, original value saved on stack (PT_AREG0)
* a1: a1
* a2: new stack pointer, original value in depc
* a3: dispatch table
* depc: a2, original value saved on stack (PT_DEPC)
* excsave_1: a3
*
* The value for PT_DEPC saved to stack also functions as a boolean to
* indicate that the exception is either a double or a regular exception:
*
* PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception
* < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
*
* Note: Neither the kernel nor the user exception handler generate literals.
*
*/
#include <linux/linkage.h>
#include <asm/ptrace.h>
#include <asm/current.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/thread_info.h>
#include <asm/vectors.h>
#define WINDOW_VECTORS_SIZE 0x180
/*
* User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0)
*
* We get here when an exception occurred while we were in userland.
* We switch to the kernel stack and jump to the first level handler
* associated to the exception cause.
*
* Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already
* decremented by PT_USER_SIZE.
*/
.section .UserExceptionVector.text, "ax"
ENTRY(_UserExceptionVector)
xsr a3, excsave1 # save a3 and get dispatch table
wsr a2, depc # save a2
l32i a2, a3, EXC_TABLE_KSTK # load kernel stack to a2
s32i a0, a2, PT_AREG0 # save a0 to ESF
rsr a0, exccause # retrieve exception cause
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3 # find entry in table
l32i a0, a0, EXC_TABLE_FAST_USER # load handler
xsr a3, excsave1 # restore a3 and dispatch table
jx a0
ENDPROC(_UserExceptionVector)
/*
* Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0)
*
* We get this exception when we were already in kernel space.
* We decrement the current stack pointer (kernel) by PT_SIZE and
* jump to the first-level handler associated with the exception cause.
*
* Note: we need to preserve space for the spill region.
*/
.section .KernelExceptionVector.text, "ax"
ENTRY(_KernelExceptionVector)
xsr a3, excsave1 # save a3, and get dispatch table
wsr a2, depc # save a2
addi a2, a1, -16-PT_SIZE # adjust stack pointer
s32i a0, a2, PT_AREG0 # save a0 to ESF
rsr a0, exccause # retrieve exception cause
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3 # find entry in table
l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address
xsr a3, excsave1 # restore a3 and dispatch table
jx a0
ENDPROC(_KernelExceptionVector)
/*
* Double exception vector (Exceptions with PS.EXCM == 1)
* We get this exception when another exception occurs while were are
* already in an exception, such as window overflow/underflow exception,
* or 'expected' exceptions, for example memory exception when we were trying
* to read data from an invalid address in user space.
*
* Note that this vector is never invoked for level-1 interrupts, because such
* interrupts are disabled (masked) when PS.EXCM is set.
*
* We decode the exception and take the appropriate action. However, the
* double exception vector is much more careful, because a lot more error
* cases go through the double exception vector than through the user and
* kernel exception vectors.
*
* Occasionally, the kernel expects a double exception to occur. This usually
* happens when accessing user-space memory with the user's permissions
* (l32e/s32e instructions). The kernel state, though, is not always suitable
* for immediate transfer of control to handle_double, where "normal" exception
* processing occurs. Also in kernel mode, TLB misses can occur if accessing
* vmalloc memory, possibly requiring repair in a double exception handler.
*
* The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as
* a boolean variable and a pointer to a fixup routine. If the variable
* EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of
* zero indicates to use the default kernel/user exception handler.
* There is only one exception, when the value is identical to the exc_table
* label, the kernel is in trouble. This mechanism is used to protect critical
* sections, mainly when the handler writes to the stack to assert the stack
* pointer is valid. Once the fixup/default handler leaves that area, the
* EXC_TABLE_FIXUP variable is reset to the fixup handler or zero.
*
* Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the
* nonzero address of a fixup routine before it could cause a double exception
* and reset it before it returns.
*
* Some other things to take care of when a fast exception handler doesn't
* specify a particular fixup handler but wants to use the default handlers:
*
* - The original stack pointer (in a1) must not be modified. The fast
* exception handler should only use a2 as the stack pointer.
*
* - If the fast handler manipulates the stack pointer (in a2), it has to
* register a valid fixup handler and cannot use the default handlers.
*
* - The handler can use any other generic register from a3 to a15, but it
* must save the content of these registers to stack (PT_AREG3...PT_AREGx)
*
* - These registers must be saved before a double exception can occur.
*
* - If we ever implement handling signals while in double exceptions, the
* number of registers a fast handler has saved (excluding a0 and a1) must
* be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. )
*
* The fixup handlers are special handlers:
*
* - Fixup entry conditions differ from regular exceptions:
*
* a0: DEPC
* a1: a1
* a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE
* a3: exctable
* depc: a0
* excsave_1: a3
*
* - When the kernel enters the fixup handler, it still assumes it is in a
* critical section, so EXC_TABLE_FIXUP variable is set to exc_table.
* The fixup handler, therefore, has to re-register itself as the fixup
* handler before it returns from the double exception.
*
* - Fixup handler can share the same exception frame with the fast handler.
* The kernel stack pointer is not changed when entering the fixup handler.
*
* - Fixup handlers can jump to the default kernel and user exception
* handlers. Before it jumps, though, it has to setup a exception frame
* on stack. Because the default handler resets the register fixup handler
* the fixup handler must make sure that the default handler returns to
* it instead of the exception address, so it can re-register itself as
* the fixup handler.
*
* In case of a critical condition where the kernel cannot recover, we jump
* to unrecoverable_exception with the following entry conditions.
* All registers a0...a15 are unchanged from the last exception, except:
*
* a0: last address before we jumped to the unrecoverable_exception.
* excsave_1: a0
*
*
* See the handle_alloca_user and spill_registers routines for example clients.
*
* FIXME: Note: we currently don't allow signal handling coming from a double
* exception, so the item markt with (*) is not required.
*/
.section .DoubleExceptionVector.text, "ax"
.begin literal_prefix .DoubleExceptionVector
.globl _DoubleExceptionVector_WindowUnderflow
.globl _DoubleExceptionVector_WindowOverflow
ENTRY(_DoubleExceptionVector)
xsr a3, excsave1
s32i a2, a3, EXC_TABLE_DOUBLE_SAVE
/* Check for kernel double exception (usually fatal). */
rsr a2, ps
_bbci.l a2, PS_UM_BIT, .Lksp
/* Check if we are currently handling a window exception. */
/* Note: We don't need to indicate that we enter a critical section. */
xsr a0, depc # get DEPC, save a0
movi a2, WINDOW_VECTORS_VADDR
_bltu a0, a2, .Lfixup
addi a2, a2, WINDOW_VECTORS_SIZE
_bgeu a0, a2, .Lfixup
/* Window overflow/underflow exception. Get stack pointer. */
l32i a2, a3, EXC_TABLE_KSTK
/* Check for overflow/underflow exception, jump if overflow. */
_bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow
/*
* Restart window underflow exception.
* Currently:
* depc = orig a0,
* a0 = orig DEPC,
* a2 = new sp based on KSTK from exc_table
* a3 = excsave_1
* excsave_1 = orig a3
*
* We return to the instruction in user space that caused the window
* underflow exception. Therefore, we change window base to the value
* before we entered the window underflow exception and prepare the
* registers to return as if we were coming from a regular exception
* by changing depc (in a0).
* Note: We can trash the current window frame (a0...a3) and depc!
*/
_DoubleExceptionVector_WindowUnderflow:
xsr a3, excsave1
wsr a2, depc # save stack pointer temporarily
rsr a0, ps
extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH
wsr a0, windowbase
rsync
/* We are now in the previous window frame. Save registers again. */
xsr a2, depc # save a2 and get stack pointer
s32i a0, a2, PT_AREG0
xsr a3, excsave1
rsr a0, exccause
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3
xsr a3, excsave1
l32i a0, a0, EXC_TABLE_FAST_USER
jx a0
/*
* We only allow the ITLB miss exception if we are in kernel space.
* All other exceptions are unexpected and thus unrecoverable!
*/
#ifdef CONFIG_MMU
.extern fast_second_level_miss_double_kernel
.Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */
rsr a3, exccause
beqi a3, EXCCAUSE_ITLB_MISS, 1f
addi a3, a3, -EXCCAUSE_DTLB_MISS
bnez a3, .Lunrecoverable
1: movi a3, fast_second_level_miss_double_kernel
jx a3
#else
.equ .Lksp, .Lunrecoverable
#endif
/* Critical! We can't handle this situation. PANIC! */
.extern unrecoverable_exception
.Lunrecoverable_fixup:
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
xsr a0, depc
.Lunrecoverable:
rsr a3, excsave1
wsr a0, excsave1
movi a0, unrecoverable_exception
callx0 a0
.Lfixup:/* Check for a fixup handler or if we were in a critical section. */
/* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave1: a3 */
/* Enter critical section. */
l32i a2, a3, EXC_TABLE_FIXUP
s32i a3, a3, EXC_TABLE_FIXUP
beq a2, a3, .Lunrecoverable_fixup # critical section
beqz a2, .Ldflt # no handler was registered
/* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */
jx a2
.Ldflt: /* Get stack pointer. */
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
addi a2, a2, -PT_USER_SIZE
/* a0: depc, a1: a1, a2: kstk, a3: exctable, depc: a0, excsave: a3 */
s32i a0, a2, PT_DEPC
l32i a0, a3, EXC_TABLE_DOUBLE_SAVE
xsr a0, depc
s32i a0, a2, PT_AREG0
/* a0: avail, a1: a1, a2: kstk, a3: exctable, depc: a2, excsave: a3 */
rsr a0, exccause
addx4 a0, a0, a3
xsr a3, excsave1
l32i a0, a0, EXC_TABLE_FAST_USER
jx a0
/*
* Restart window OVERFLOW exception.
* Currently:
* depc = orig a0,
* a0 = orig DEPC,
* a2 = new sp based on KSTK from exc_table
* a3 = EXCSAVE_1
* excsave_1 = orig a3
*
* We return to the instruction in user space that caused the window
* overflow exception. Therefore, we change window base to the value
* before we entered the window overflow exception and prepare the
* registers to return as if we were coming from a regular exception
* by changing DEPC (in a0).
*
* NOTE: We CANNOT trash the current window frame (a0...a3), but we
* can clobber depc.
*
* The tricky part here is that overflow8 and overflow12 handlers
* save a0, then clobber a0. To restart the handler, we have to restore
* a0 if the double exception was past the point where a0 was clobbered.
*
* To keep things simple, we take advantage of the fact all overflow
* handlers save a0 in their very first instruction. If DEPC was past
* that instruction, we can safely restore a0 from where it was saved
* on the stack.
*
* a0: depc, a1: a1, a2: kstk, a3: exc_table, depc: a0, excsave1: a3
*/
_DoubleExceptionVector_WindowOverflow:
extui a2, a0, 0, 6 # get offset into 64-byte vector handler
beqz a2, 1f # if at start of vector, don't restore
addi a0, a0, -128
bbsi a0, 8, 1f # don't restore except for overflow 8 and 12
bbsi a0, 7, 2f
/*
* Restore a0 as saved by _WindowOverflow8().
*
* FIXME: we really need a fixup handler for this L32E,
* for the extremely unlikely case where the overflow handler's
* reference thru a0 gets a hardware TLB refill that bumps out
* the (distinct, aliasing) TLB entry that mapped its prior
* references thru a9, and where our reference now thru a9
* gets a 2nd-level miss exception (not hardware TLB refill).
*/
l32e a2, a9, -16
wsr a2, depc # replace the saved a0
j 1f
2:
/*
* Restore a0 as saved by _WindowOverflow12().
*
* FIXME: we really need a fixup handler for this L32E,
* for the extremely unlikely case where the overflow handler's
* reference thru a0 gets a hardware TLB refill that bumps out
* the (distinct, aliasing) TLB entry that mapped its prior
* references thru a13, and where our reference now thru a13
* gets a 2nd-level miss exception (not hardware TLB refill).
*/
l32e a2, a13, -16
wsr a2, depc # replace the saved a0
1:
/*
* Restore WindowBase while leaving all address registers restored.
* We have to use ROTW for this, because WSR.WINDOWBASE requires
* an address register (which would prevent restore).
*
* Window Base goes from 0 ... 7 (Module 8)
* Window Start is 8 bits; Ex: (0b1010 1010):0x55 from series of call4s
*/
rsr a0, ps
extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH
rsr a2, windowbase
sub a0, a2, a0
extui a0, a0, 0, 3
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
xsr a3, excsave1
beqi a0, 1, .L1pane
beqi a0, 3, .L3pane
rsr a0, depc
rotw -2
/*
* We are now in the user code's original window frame.
* Process the exception as a user exception as if it was
* taken by the user code.
*
* This is similar to the user exception vector,
* except that PT_DEPC isn't set to EXCCAUSE.
*/
1:
xsr a3, excsave1
wsr a2, depc
l32i a2, a3, EXC_TABLE_KSTK
s32i a0, a2, PT_AREG0
rsr a0, exccause
s32i a0, a2, PT_DEPC
addx4 a0, a0, a3
l32i a0, a0, EXC_TABLE_FAST_USER
xsr a3, excsave1
jx a0
.L1pane:
rsr a0, depc
rotw -1
j 1b
.L3pane:
rsr a0, depc
rotw -3
j 1b
.end literal_prefix
ENDPROC(_DoubleExceptionVector)
/*
* Debug interrupt vector
*
* There is not much space here, so simply jump to another handler.
* EXCSAVE[DEBUGLEVEL] has been set to that handler.
*/
.section .DebugInterruptVector.text, "ax"
ENTRY(_DebugInterruptVector)
xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL
jx a0
ENDPROC(_DebugInterruptVector)
/*
* Medium priority level interrupt vectors
*
* Each takes less than 16 (0x10) bytes, no literals, by placing
* the extra 8 bytes that would otherwise be required in the window
* vectors area where there is space. With relocatable vectors,
* all vectors are within ~ 4 kB range of each other, so we can
* simply jump (J) to another vector without having to use JX.
*
* common_exception code gets current IRQ level in PS.INTLEVEL
* and preserves it for the IRQ handling time.
*/
.macro irq_entry_level level
.if XCHAL_EXCM_LEVEL >= \level
.section .Level\level\()InterruptVector.text, "ax"
ENTRY(_Level\level\()InterruptVector)
wsr a0, excsave2
rsr a0, epc\level
wsr a0, epc1
movi a0, EXCCAUSE_LEVEL1_INTERRUPT
wsr a0, exccause
rsr a0, eps\level
# branch to user or kernel vector
j _SimulateUserKernelVectorException
.endif
.endm
irq_entry_level 2
irq_entry_level 3
irq_entry_level 4
irq_entry_level 5
irq_entry_level 6
/* Window overflow and underflow handlers.
* The handlers must be 64 bytes apart, first starting with the underflow
* handlers underflow-4 to underflow-12, then the overflow handlers
* overflow-4 to overflow-12.
*
* Note: We rerun the underflow handlers if we hit an exception, so
* we try to access any page that would cause a page fault early.
*/
#define ENTRY_ALIGN64(name) \
.globl name; \
.align 64; \
name:
.section .WindowVectors.text, "ax"
/* 4-Register Window Overflow Vector (Handler) */
ENTRY_ALIGN64(_WindowOverflow4)
s32e a0, a5, -16
s32e a1, a5, -12
s32e a2, a5, -8
s32e a3, a5, -4
rfwo
ENDPROC(_WindowOverflow4)
#if XCHAL_EXCM_LEVEL >= 2
/* Not a window vector - but a convenient location
* (where we know there's space) for continuation of
* medium priority interrupt dispatch code.
* On entry here, a0 contains PS, and EPC2 contains saved a0:
*/
.align 4
_SimulateUserKernelVectorException:
addi a0, a0, (1 << PS_EXCM_BIT)
wsr a0, ps
bbsi.l a0, PS_UM_BIT, 1f # branch if user mode
rsr a0, excsave2 # restore a0
j _KernelExceptionVector # simulate kernel vector exception
1: rsr a0, excsave2 # restore a0
j _UserExceptionVector # simulate user vector exception
#endif
/* 4-Register Window Underflow Vector (Handler) */
ENTRY_ALIGN64(_WindowUnderflow4)
l32e a0, a5, -16
l32e a1, a5, -12
l32e a2, a5, -8
l32e a3, a5, -4
rfwu
ENDPROC(_WindowUnderflow4)
/* 8-Register Window Overflow Vector (Handler) */
ENTRY_ALIGN64(_WindowOverflow8)
s32e a0, a9, -16
l32e a0, a1, -12
s32e a2, a9, -8
s32e a1, a9, -12
s32e a3, a9, -4
s32e a4, a0, -32
s32e a5, a0, -28
s32e a6, a0, -24
s32e a7, a0, -20
rfwo
ENDPROC(_WindowOverflow8)
/* 8-Register Window Underflow Vector (Handler) */
ENTRY_ALIGN64(_WindowUnderflow8)
l32e a1, a9, -12
l32e a0, a9, -16
l32e a7, a1, -12
l32e a2, a9, -8
l32e a4, a7, -32
l32e a3, a9, -4
l32e a5, a7, -28
l32e a6, a7, -24
l32e a7, a7, -20
rfwu
ENDPROC(_WindowUnderflow8)
/* 12-Register Window Overflow Vector (Handler) */
ENTRY_ALIGN64(_WindowOverflow12)
s32e a0, a13, -16
l32e a0, a1, -12
s32e a1, a13, -12
s32e a2, a13, -8
s32e a3, a13, -4
s32e a4, a0, -48
s32e a5, a0, -44
s32e a6, a0, -40
s32e a7, a0, -36
s32e a8, a0, -32
s32e a9, a0, -28
s32e a10, a0, -24
s32e a11, a0, -20
rfwo
ENDPROC(_WindowOverflow12)
/* 12-Register Window Underflow Vector (Handler) */
ENTRY_ALIGN64(_WindowUnderflow12)
l32e a1, a13, -12
l32e a0, a13, -16
l32e a11, a1, -12
l32e a2, a13, -8
l32e a4, a11, -48
l32e a8, a11, -32
l32e a3, a13, -4
l32e a5, a11, -44
l32e a6, a11, -40
l32e a7, a11, -36
l32e a9, a11, -28
l32e a10, a11, -24
l32e a11, a11, -20
rfwu
ENDPROC(_WindowUnderflow12)
.text
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