Commit 17290231 authored by Max Filippov's avatar Max Filippov
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xtensa: add fixup for double exception raised in window overflow



There are two FIXMEs in the double exception handler 'for the extremely
unlikely case'. This case gets hit by gcc during kernel build once in
a few hours, resulting in an unrecoverable exception condition.

Provide missing fixup routine to handle this case. Double exception
literals now need 8 more bytes, add them to the linker script.

Also replace bbsi instructions with bbsi.l as we're branching depending
on 8th and 7th LSB-based bits of exception address.

This may be tested by adding the explicit DTLB invalidation to window
overflow handlers, like the following:

    --- a/arch/xtensa/kernel/vectors.S
    +++ b/arch/xtensa/kernel/vectors.S
    @@ -592,6 +592,14 @@ ENDPROC(_WindowUnderflow4)
     ENTRY_ALIGN64(_WindowOverflow8)

    	s32e	a0, a9, -16
    +	bbsi.l	a9, 31, 1f
    +	rsr	a0, ccount
    +	bbsi.l	a0, 4, 1f
    +	pdtlb	a0, a9
    +	idtlb	a0
    +	movi	a0, 9
    +	idtlb	a0
    +1:
    	l32e    a0, a1, -12
    	s32e    a2, a9,  -8
    	s32e    a1, a9, -12

Cc: stable@vger.kernel.org
Signed-off-by: default avatarMax Filippov <jcmvbkbc@gmail.com>
parent 1860e379
......@@ -376,38 +376,42 @@ _DoubleExceptionVector_WindowOverflow:
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
bbsi.l a0, 8, 1f # don't restore except for overflow 8 and 12
/*
* This fixup handler is 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/a13, and where our reference now thru
* a9/a13 gets a 2nd-level miss exception (not hardware TLB refill).
*/
movi a2, window_overflow_restore_a0_fixup
s32i a2, a3, EXC_TABLE_FIXUP
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
xsr a3, excsave1
bbsi.l 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
l32e a0, a9, -16
wsr a0, depc # replace the saved a0
j 3f
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
l32e a0, a13, -16
wsr a0, depc # replace the saved a0
3:
xsr a3, excsave1
movi a0, 0
s32i a0, a3, EXC_TABLE_FIXUP
s32i a2, a3, EXC_TABLE_DOUBLE_SAVE
1:
/*
* Restore WindowBase while leaving all address registers restored.
......@@ -449,6 +453,7 @@ _DoubleExceptionVector_WindowOverflow:
s32i a0, a2, PT_DEPC
_DoubleExceptionVector_handle_exception:
addx4 a0, a0, a3
l32i a0, a0, EXC_TABLE_FAST_USER
xsr a3, excsave1
......@@ -464,10 +469,119 @@ _DoubleExceptionVector_WindowOverflow:
rotw -3
j 1b
.end literal_prefix
ENDPROC(_DoubleExceptionVector)
/*
* Fixup handler for TLB miss in double exception handler for window owerflow.
* We get here with windowbase set to the window that was being spilled and
* a0 trashed. a0 bit 7 determines if this is a call8 (bit clear) or call12
* (bit set) window.
*
* We do the following here:
* - go to the original window retaining a0 value;
* - set up exception stack to return back to appropriate a0 restore code
* (we'll need to rotate window back and there's no place to save this
* information, use different return address for that);
* - handle the exception;
* - go to the window that was being spilled;
* - set up window_overflow_restore_a0_fixup as a fixup routine;
* - reload a0;
* - restore the original window;
* - reset the default fixup routine;
* - return to user. By the time we get to this fixup handler all information
* about the conditions of the original double exception that happened in
* the window overflow handler is lost, so we just return to userspace to
* retry overflow from start.
*
* a0: value of depc, original value in depc
* a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE
* a3: exctable, original value in excsave1
*/
ENTRY(window_overflow_restore_a0_fixup)
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, .Lhandle_1
_beqi a0, 3, .Lhandle_3
.macro overflow_fixup_handle_exception_pane n
rsr a0, depc
rotw -\n
xsr a3, excsave1
wsr a2, depc
l32i a2, a3, EXC_TABLE_KSTK
s32i a0, a2, PT_AREG0
movi a0, .Lrestore_\n
s32i a0, a2, PT_DEPC
rsr a0, exccause
j _DoubleExceptionVector_handle_exception
.endm
overflow_fixup_handle_exception_pane 2
.Lhandle_1:
overflow_fixup_handle_exception_pane 1
.Lhandle_3:
overflow_fixup_handle_exception_pane 3
.macro overflow_fixup_restore_a0_pane n
rotw \n
/* Need to preserve a0 value here to be able to handle exception
* that may occur on a0 reload from stack. It may occur because
* TLB miss handler may not be atomic and pointer to page table
* may be lost before we get here. There are no free registers,
* so we need to use EXC_TABLE_DOUBLE_SAVE area.
*/
xsr a3, excsave1
s32i a2, a3, EXC_TABLE_DOUBLE_SAVE
movi a2, window_overflow_restore_a0_fixup
s32i a2, a3, EXC_TABLE_FIXUP
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
xsr a3, excsave1
bbsi.l a0, 7, 1f
l32e a0, a9, -16
j 2f
1:
l32e a0, a13, -16
2:
rotw -\n
.endm
.Lrestore_2:
overflow_fixup_restore_a0_pane 2
.Lset_default_fixup:
xsr a3, excsave1
s32i a2, a3, EXC_TABLE_DOUBLE_SAVE
movi a2, 0
s32i a2, a3, EXC_TABLE_FIXUP
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
xsr a3, excsave1
rfe
.Lrestore_1:
overflow_fixup_restore_a0_pane 1
j .Lset_default_fixup
.Lrestore_3:
overflow_fixup_restore_a0_pane 3
j .Lset_default_fixup
ENDPROC(window_overflow_restore_a0_fixup)
.end literal_prefix
/*
* Debug interrupt vector
*
......
......@@ -269,13 +269,13 @@ SECTIONS
.UserExceptionVector.literal)
SECTION_VECTOR (_DoubleExceptionVector_literal,
.DoubleExceptionVector.literal,
DOUBLEEXC_VECTOR_VADDR - 16,
DOUBLEEXC_VECTOR_VADDR - 40,
SIZEOF(.UserExceptionVector.text),
.UserExceptionVector.text)
SECTION_VECTOR (_DoubleExceptionVector_text,
.DoubleExceptionVector.text,
DOUBLEEXC_VECTOR_VADDR,
32,
40,
.DoubleExceptionVector.literal)
. = (LOADADDR( .DoubleExceptionVector.text ) + SIZEOF( .DoubleExceptionVector.text ) + 3) & ~ 3;
......
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