[Xen-devel] [PATCH] xen: fix alignment for bitops

[Vladimir Murzin <murzin.v@xxxxxxxxx>]

Bitops operations like set/clear/change mandate world aligned pointer, mainly
because architectures specific implementation.

Looks that DEFINE_PER_CPU does required alignment for cpu_control_block;
however, local copy used for bitops might not be world aligned.

For arm64 it ends up with unaligned access trap:

Unhandled fault: alignment fault (0x96000021) at 0xffffffc01cf07d64
Internal error: : 96000021 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 563 Comm: udevd Not tainted 3.14.0+ #1
task: ffffffc01de95c40 ti: ffffffc01cf04000 task.ti: ffffffc01cf04000
PC is at clear_bit+0x14/0x30
LR is at evtchn_fifo_handle_events+0x168/0x184
pc : [<ffffffc00027b6c4>] lr : [<ffffffc0002b17d8>] pstate: 600001c5
sp : ffffffc01cf07d00
x29: ffffffc01cf07d00 x28: ffffffc01dce5000
x27: 0000000000000008 x26: 0000000000000002
x25: 00000000dffe0000 x24: 0000000000000000
x23: 0000000000000007 x22: ffffffc000660000
x21: ffffffc00060d900 x20: ffffffc01efdd900
x19: ffffffc01dc26000 x18: 0000007ff1d5a570
x17: 0000007faf848824 x16: 000000000044bf10
x15: 0000007faf8ed598 x14: ffffffffffffffff
x13: 0000000000000028 x12: 0101010101010101
x11: 7f7f7f7f7f7f7f7f x10: 622e607360632e75
x9 : 7f7f7f7f7f7f7f7f x8 : 000000001e9d0000
x7 : ffffffc01d800120 x6 : 00000000a0000000
x5 : 00000000a0000000 x4 : 0000000000000000
x3 : 0000000000000080 x2 : 0000000000000001
x1 : ffffffc01cf07d64 x0 : 0000000000000000

Process udevd (pid: 563, stack limit = 0xffffffc01cf04058)
Stack: (0xffffffc01cf07d00 to 0xffffffc01cf08000)
7d00: 1cf07d80 ffffffc0 002aeb7c ffffffc0 0060d6ec ffffffc0 1efe1c90 ffffffc0
7d20: 0056e418 ffffffc0 0066c000 ffffffc0 00000000 00000000 005659a0 ffffffc0
7d40: 00565998 ffffffc0 004053b0 00000000 00423bb0 00000000 00423000 00000000
7d60: a0000000 00000080 002aeb1c ffffffc0 00000000 00000000 002aeb4c ffffffc0
7d80: 1cf07dd0 ffffffc0 002aec2c ffffffc0 1dc09f00 ffffffc0 00630360 ffffffc0
7da0: 1dc23400 ffffffc0 00567c08 ffffffc0 0000001f 00000000 1efdc400 ffffffc0
7dc0: 000001ed 00000000 004053b0 00000000 1cf07de0 ffffffc0 00092eec ffffffc0
7de0: 1cf07df0 ffffffc0 000d79bc ffffffc0 1cf07e30 ffffffc0 000d3cf0 ffffffc0
7e00: 0000001f 00000000 0060d000 ffffffc0 00565000 ffffffc0 00565000 ffffffc0
7e20: 0000001f 00000000 00000000 00000000 1cf07e50 ffffffc0 000848bc ffffffc0
7e40: 0060d5a0 ffffffc0 000848a4 ffffffc0 1cf07ea0 ffffffc0 0008128c ffffffc0
7e60: 00667000 ffffffc0 0000400c ffffff80 1cf07ed0 ffffffc0 00004010 ffffff80
7e80: 80000000 00000000 2dca8010 00000000 1cf07ed0 ffffffc0 00000012 00000000
7ea0: f1d5b710 0000007f 000841bc ffffffc0 2dca8170 00000000 f1d5b870 0000007f
7ec0: ffffffff ffffffff af848838 0000007f 00000000 00000000 f1d5b7a0 0000007f
7ee0: f1d5b720 0000007f 00000000 00000000 61642f76 632f6174 2e353a34 00706d74
7f00: f1d5b7ae 0000007f 00000000 00000000 0000004f 00000000 7f7f7f7f 7f7f7f7f
7f20: 60632e75 622e6073 7f7f7f7f 7f7f7f7f 01010101 01010101 00000028 00000000
7f40: ffffffff ffffffff af8ed598 0000007f 0044bf10 00000000 af848824 0000007f
7f60: f1d5a570 0000007f 2dca8170 00000000 f1d5b870 0000007f 2dcc6ca0 00000000
7f80: f1d5bc70 0000007f 00000000 00000000 2dca8010 00000000 000001ed 00000000
7fa0: 004053b0 00000000 00423bb0 00000000 00423000 00000000 f1d5b710 0000007f
7fc0: 0041f460 00000000 f1d5b710 0000007f af848838 0000007f 80000000 00000000
7fe0: ffffff9c ffffffff ffffffff ffffffff dfdfdfcf cfdfdfdf dfdfdfcf cfdfdfdf
Call trace:
[<ffffffc00027b6c4>] clear_bit+0x14/0x30
[<ffffffc0002aeb78>] __xen_evtchn_do_upcall+0x9c/0x144
[<ffffffc0002aec28>] xen_hvm_evtchn_do_upcall+0x8/0x14
[<ffffffc000092ee8>] xen_arm_callback+0x8/0x18
[<ffffffc0000d79b8>] handle_percpu_devid_irq+0x90/0xb8
[<ffffffc0000d3cec>] generic_handle_irq+0x24/0x40
[<ffffffc0000848b8>] handle_IRQ+0x68/0xe0
[<ffffffc000081288>] gic_handle_irq+0x38/0x80
Exception stack(0xffffffc01cf07eb0 to 0xffffffc01cf07fd0)
7ea0:                                     2dca8170 00000000 f1d5b870 0000007f
7ec0: ffffffff ffffffff af848838 0000007f 00000000 00000000 f1d5b7a0 0000007f
7ee0: f1d5b720 0000007f 00000000 00000000 61642f76 632f6174 2e353a34 00706d74
7f00: f1d5b7ae 0000007f 00000000 00000000 0000004f 00000000 7f7f7f7f 7f7f7f7f
7f20: 60632e75 622e6073 7f7f7f7f 7f7f7f7f 01010101 01010101 00000028 00000000
7f40: ffffffff ffffffff af8ed598 0000007f 0044bf10 00000000 af848824 0000007f
7f60: f1d5a570 0000007f 2dca8170 00000000 f1d5b870 0000007f 2dcc6ca0 00000000
7f80: f1d5bc70 0000007f 00000000 00000000 2dca8010 00000000 000001ed 00000000
7fa0: 004053b0 00000000 00423bb0 00000000 00423000 00000000 f1d5b710 0000007f
7fc0: 0041f460 00000000 f1d5b710 0000007f
Code: 4a030000 d2800022 8b400c21 9ac32043 (c85f7c22)

Instruct compiler to keep local copy of "ready" world aligned.

Signed-off-by: Vladimir Murzin <murzin.v@xxxxxxxxx>
---
 I'd appreciate any thought how to fix it in the right way if suggest patch
 doesn't look appropriate ;) 

 drivers/xen/events/events_fifo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 96109a9..291c4a8 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -285,7 +285,7 @@ static void consume_one_event(unsigned cpu,
 static void evtchn_fifo_handle_events(unsigned cpu)
 {
        struct evtchn_fifo_control_block *control_block;
-       uint32_t ready;
+       uint32_t __aligned(sizeof(long)) ready;
        unsigned q;
 
        control_block = per_cpu(cpu_control_block, cpu);
-- 
1.8.3.2


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