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da1ce37e GKH |
1 | From 17290231df16eeee5dfc198dbf5ee4b419996dcd Mon Sep 17 00:00:00 2001 |
2 | From: Max Filippov <jcmvbkbc@gmail.com> | |
3 | Date: Sat, 24 May 2014 21:48:28 +0400 | |
4 | Subject: xtensa: add fixup for double exception raised in window overflow | |
5 | ||
6 | From: Max Filippov <jcmvbkbc@gmail.com> | |
7 | ||
8 | commit 17290231df16eeee5dfc198dbf5ee4b419996dcd upstream. | |
9 | ||
10 | There are two FIXMEs in the double exception handler 'for the extremely | |
11 | unlikely case'. This case gets hit by gcc during kernel build once in | |
12 | a few hours, resulting in an unrecoverable exception condition. | |
13 | ||
14 | Provide missing fixup routine to handle this case. Double exception | |
15 | literals now need 8 more bytes, add them to the linker script. | |
16 | ||
17 | Also replace bbsi instructions with bbsi.l as we're branching depending | |
18 | on 8th and 7th LSB-based bits of exception address. | |
19 | ||
20 | This may be tested by adding the explicit DTLB invalidation to window | |
21 | overflow handlers, like the following: | |
22 | ||
23 | # --- a/arch/xtensa/kernel/vectors.S | |
24 | # +++ b/arch/xtensa/kernel/vectors.S | |
25 | # @@ -592,6 +592,14 @@ ENDPROC(_WindowUnderflow4) | |
26 | # ENTRY_ALIGN64(_WindowOverflow8) | |
27 | # | |
28 | # s32e a0, a9, -16 | |
29 | # + bbsi.l a9, 31, 1f | |
30 | # + rsr a0, ccount | |
31 | # + bbsi.l a0, 4, 1f | |
32 | # + pdtlb a0, a9 | |
33 | # + idtlb a0 | |
34 | # + movi a0, 9 | |
35 | # + idtlb a0 | |
36 | # +1: | |
37 | # l32e a0, a1, -12 | |
38 | # s32e a2, a9, -8 | |
39 | # s32e a1, a9, -12 | |
40 | ||
41 | Signed-off-by: Max Filippov <jcmvbkbc@gmail.com> | |
42 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
43 | ||
44 | --- | |
45 | arch/xtensa/kernel/vectors.S | 158 +++++++++++++++++++++++++++++++++------ | |
46 | arch/xtensa/kernel/vmlinux.lds.S | 4 | |
47 | 2 files changed, 138 insertions(+), 24 deletions(-) | |
48 | ||
49 | --- a/arch/xtensa/kernel/vectors.S | |
50 | +++ b/arch/xtensa/kernel/vectors.S | |
51 | @@ -376,38 +376,42 @@ _DoubleExceptionVector_WindowOverflow: | |
52 | beqz a2, 1f # if at start of vector, don't restore | |
53 | ||
54 | addi a0, a0, -128 | |
55 | - bbsi a0, 8, 1f # don't restore except for overflow 8 and 12 | |
56 | - bbsi a0, 7, 2f | |
57 | + bbsi.l a0, 8, 1f # don't restore except for overflow 8 and 12 | |
58 | + | |
59 | + /* | |
60 | + * This fixup handler is for the extremely unlikely case where the | |
61 | + * overflow handler's reference thru a0 gets a hardware TLB refill | |
62 | + * that bumps out the (distinct, aliasing) TLB entry that mapped its | |
63 | + * prior references thru a9/a13, and where our reference now thru | |
64 | + * a9/a13 gets a 2nd-level miss exception (not hardware TLB refill). | |
65 | + */ | |
66 | + movi a2, window_overflow_restore_a0_fixup | |
67 | + s32i a2, a3, EXC_TABLE_FIXUP | |
68 | + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
69 | + xsr a3, excsave1 | |
70 | + | |
71 | + bbsi.l a0, 7, 2f | |
72 | ||
73 | /* | |
74 | * Restore a0 as saved by _WindowOverflow8(). | |
75 | - * | |
76 | - * FIXME: we really need a fixup handler for this L32E, | |
77 | - * for the extremely unlikely case where the overflow handler's | |
78 | - * reference thru a0 gets a hardware TLB refill that bumps out | |
79 | - * the (distinct, aliasing) TLB entry that mapped its prior | |
80 | - * references thru a9, and where our reference now thru a9 | |
81 | - * gets a 2nd-level miss exception (not hardware TLB refill). | |
82 | */ | |
83 | ||
84 | - l32e a2, a9, -16 | |
85 | - wsr a2, depc # replace the saved a0 | |
86 | - j 1f | |
87 | + l32e a0, a9, -16 | |
88 | + wsr a0, depc # replace the saved a0 | |
89 | + j 3f | |
90 | ||
91 | 2: | |
92 | /* | |
93 | * Restore a0 as saved by _WindowOverflow12(). | |
94 | - * | |
95 | - * FIXME: we really need a fixup handler for this L32E, | |
96 | - * for the extremely unlikely case where the overflow handler's | |
97 | - * reference thru a0 gets a hardware TLB refill that bumps out | |
98 | - * the (distinct, aliasing) TLB entry that mapped its prior | |
99 | - * references thru a13, and where our reference now thru a13 | |
100 | - * gets a 2nd-level miss exception (not hardware TLB refill). | |
101 | */ | |
102 | ||
103 | - l32e a2, a13, -16 | |
104 | - wsr a2, depc # replace the saved a0 | |
105 | + l32e a0, a13, -16 | |
106 | + wsr a0, depc # replace the saved a0 | |
107 | +3: | |
108 | + xsr a3, excsave1 | |
109 | + movi a0, 0 | |
110 | + s32i a0, a3, EXC_TABLE_FIXUP | |
111 | + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
112 | 1: | |
113 | /* | |
114 | * Restore WindowBase while leaving all address registers restored. | |
115 | @@ -449,6 +453,7 @@ _DoubleExceptionVector_WindowOverflow: | |
116 | ||
117 | s32i a0, a2, PT_DEPC | |
118 | ||
119 | +_DoubleExceptionVector_handle_exception: | |
120 | addx4 a0, a0, a3 | |
121 | l32i a0, a0, EXC_TABLE_FAST_USER | |
122 | xsr a3, excsave1 | |
123 | @@ -464,11 +469,120 @@ _DoubleExceptionVector_WindowOverflow: | |
124 | rotw -3 | |
125 | j 1b | |
126 | ||
127 | - .end literal_prefix | |
128 | ||
129 | ENDPROC(_DoubleExceptionVector) | |
130 | ||
131 | /* | |
132 | + * Fixup handler for TLB miss in double exception handler for window owerflow. | |
133 | + * We get here with windowbase set to the window that was being spilled and | |
134 | + * a0 trashed. a0 bit 7 determines if this is a call8 (bit clear) or call12 | |
135 | + * (bit set) window. | |
136 | + * | |
137 | + * We do the following here: | |
138 | + * - go to the original window retaining a0 value; | |
139 | + * - set up exception stack to return back to appropriate a0 restore code | |
140 | + * (we'll need to rotate window back and there's no place to save this | |
141 | + * information, use different return address for that); | |
142 | + * - handle the exception; | |
143 | + * - go to the window that was being spilled; | |
144 | + * - set up window_overflow_restore_a0_fixup as a fixup routine; | |
145 | + * - reload a0; | |
146 | + * - restore the original window; | |
147 | + * - reset the default fixup routine; | |
148 | + * - return to user. By the time we get to this fixup handler all information | |
149 | + * about the conditions of the original double exception that happened in | |
150 | + * the window overflow handler is lost, so we just return to userspace to | |
151 | + * retry overflow from start. | |
152 | + * | |
153 | + * a0: value of depc, original value in depc | |
154 | + * a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE | |
155 | + * a3: exctable, original value in excsave1 | |
156 | + */ | |
157 | + | |
158 | +ENTRY(window_overflow_restore_a0_fixup) | |
159 | + | |
160 | + rsr a0, ps | |
161 | + extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH | |
162 | + rsr a2, windowbase | |
163 | + sub a0, a2, a0 | |
164 | + extui a0, a0, 0, 3 | |
165 | + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
166 | + xsr a3, excsave1 | |
167 | + | |
168 | + _beqi a0, 1, .Lhandle_1 | |
169 | + _beqi a0, 3, .Lhandle_3 | |
170 | + | |
171 | + .macro overflow_fixup_handle_exception_pane n | |
172 | + | |
173 | + rsr a0, depc | |
174 | + rotw -\n | |
175 | + | |
176 | + xsr a3, excsave1 | |
177 | + wsr a2, depc | |
178 | + l32i a2, a3, EXC_TABLE_KSTK | |
179 | + s32i a0, a2, PT_AREG0 | |
180 | + | |
181 | + movi a0, .Lrestore_\n | |
182 | + s32i a0, a2, PT_DEPC | |
183 | + rsr a0, exccause | |
184 | + j _DoubleExceptionVector_handle_exception | |
185 | + | |
186 | + .endm | |
187 | + | |
188 | + overflow_fixup_handle_exception_pane 2 | |
189 | +.Lhandle_1: | |
190 | + overflow_fixup_handle_exception_pane 1 | |
191 | +.Lhandle_3: | |
192 | + overflow_fixup_handle_exception_pane 3 | |
193 | + | |
194 | + .macro overflow_fixup_restore_a0_pane n | |
195 | + | |
196 | + rotw \n | |
197 | + /* Need to preserve a0 value here to be able to handle exception | |
198 | + * that may occur on a0 reload from stack. It may occur because | |
199 | + * TLB miss handler may not be atomic and pointer to page table | |
200 | + * may be lost before we get here. There are no free registers, | |
201 | + * so we need to use EXC_TABLE_DOUBLE_SAVE area. | |
202 | + */ | |
203 | + xsr a3, excsave1 | |
204 | + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
205 | + movi a2, window_overflow_restore_a0_fixup | |
206 | + s32i a2, a3, EXC_TABLE_FIXUP | |
207 | + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
208 | + xsr a3, excsave1 | |
209 | + bbsi.l a0, 7, 1f | |
210 | + l32e a0, a9, -16 | |
211 | + j 2f | |
212 | +1: | |
213 | + l32e a0, a13, -16 | |
214 | +2: | |
215 | + rotw -\n | |
216 | + | |
217 | + .endm | |
218 | + | |
219 | +.Lrestore_2: | |
220 | + overflow_fixup_restore_a0_pane 2 | |
221 | + | |
222 | +.Lset_default_fixup: | |
223 | + xsr a3, excsave1 | |
224 | + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
225 | + movi a2, 0 | |
226 | + s32i a2, a3, EXC_TABLE_FIXUP | |
227 | + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE | |
228 | + xsr a3, excsave1 | |
229 | + rfe | |
230 | + | |
231 | +.Lrestore_1: | |
232 | + overflow_fixup_restore_a0_pane 1 | |
233 | + j .Lset_default_fixup | |
234 | +.Lrestore_3: | |
235 | + overflow_fixup_restore_a0_pane 3 | |
236 | + j .Lset_default_fixup | |
237 | + | |
238 | +ENDPROC(window_overflow_restore_a0_fixup) | |
239 | + | |
240 | + .end literal_prefix | |
241 | +/* | |
242 | * Debug interrupt vector | |
243 | * | |
244 | * There is not much space here, so simply jump to another handler. | |
245 | --- a/arch/xtensa/kernel/vmlinux.lds.S | |
246 | +++ b/arch/xtensa/kernel/vmlinux.lds.S | |
247 | @@ -269,13 +269,13 @@ SECTIONS | |
248 | .UserExceptionVector.literal) | |
249 | SECTION_VECTOR (_DoubleExceptionVector_literal, | |
250 | .DoubleExceptionVector.literal, | |
251 | - DOUBLEEXC_VECTOR_VADDR - 16, | |
252 | + DOUBLEEXC_VECTOR_VADDR - 40, | |
253 | SIZEOF(.UserExceptionVector.text), | |
254 | .UserExceptionVector.text) | |
255 | SECTION_VECTOR (_DoubleExceptionVector_text, | |
256 | .DoubleExceptionVector.text, | |
257 | DOUBLEEXC_VECTOR_VADDR, | |
258 | - 32, | |
259 | + 40, | |
260 | .DoubleExceptionVector.literal) | |
261 | ||
262 | . = (LOADADDR( .DoubleExceptionVector.text ) + SIZEOF( .DoubleExceptionVector.text ) + 3) & ~ 3; |