Re: [Xen-devel] [PATCH v2] xen: fix alignment for bitops

[Vladimir Murzin <murzin.v@xxxxxxxxx>]

On Wed, Apr 16, 2014 at 8:55 AM, Vladimir Murzin <murzin.v@xxxxxxxxx> wrote:
> 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)
>
> Use unsigned long for "ready" to make sure it is world aligned.
>
> Signed-off-by: Vladimir Murzin <murzin.v@xxxxxxxxx>
> ---
>  Changes:
>  v1->v2
>     use unsigned long instead of align attribute
>
>  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;
> +       unsigned long ready;
>         unsigned q;
>
>         control_block = per_cpu(cpu_control_block, cpu);
> --
> 1.8.3.2
>

My bad :( It triggers a warning...

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