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

[Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>]

Hi Vladimir/David,

On 17 April 2014 15:52, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 16/04/14 08:55, Vladimir Murzin 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...
>
> Thanks.  Does this version work for you?
>
> David
>
> 8<----------------------
> xen/events/fifo: fix alignment for bitops on local ready word
>
> Bitops operations like set_bit(), clear_bit(), and test_bit() require
> word aligned pointers, because of architectures specific
> implementations.
>
> Looks that DEFINE_PER_CPU does required alignment for
> cpu_control_block; however, local copy of the ready word might not be
> word aligned.
>
> For arm64 it ends up with unaligned access trap at:
>
>     if (head == 0)
>         clear_bit(priority, BM(ready));
>
> Use unsigned long for "ready" to make sure it is word aligned.
>
> Signed-off-by: Vladimir Murzin <murzin.v@xxxxxxxxx>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx
> ---
>  drivers/xen/events/events_fifo.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/events/events_fifo.c 
> b/drivers/xen/events/events_fifo.c
> index 96109a9..475d967 100644
> --- a/drivers/xen/events/events_fifo.c
> +++ b/drivers/xen/events/events_fifo.c
> @@ -243,7 +243,7 @@ static void handle_irq_for_port(unsigned port)
>
>  static void consume_one_event(unsigned cpu,
>                               struct evtchn_fifo_control_block *control_block,
> -                             unsigned priority, uint32_t *ready)
> +                             unsigned priority, unsigned long *ready)
>  {
>         struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
>         uint32_t head;
> @@ -273,7 +273,7 @@ static void consume_one_event(unsigned cpu,
>          * copy of the ready word.
>          */
>         if (head == 0)
> -               clear_bit(priority, BM(ready));
> +               clear_bit(priority, ready);
>
>         if (sync_test_bit(EVTCHN_FIFO_PENDING, BM(word))
>             && !sync_test_bit(EVTCHN_FIFO_MASKED, BM(word)))
> @@ -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);
>
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> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

I have tried this fix on APM X-Gene and it is solving a crash (you
have reported) during booting of DOM0.

But while trying out domU when I tried to execute
"/etc/init.d/xencommons start || true"
I am observing a similar "alignment fault" crash  while performing
"clear_bit" in " evtchn_fifo_clear_pending"
Pasting a crash log:

root@arm64:~/xen-images# /etc/init.d/xencommons start || true
Starting C xenstored....
Unhandled fault: alignment fault (0x96000021) at 0xffffffc0fae7700c
Internal error: : 96000021 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.15.0-rc1-next-20140417+ #5
task: ffffffc0007188b0 ti: ffffffc00070c000 task.ti: ffffffc00070c000
PC is at clear_bit+0x14/0x30
LR is at evtchn_fifo_clear_pending+0x28/0x30
pc : [<ffffffc000289304>] lr : [<ffffffc0002d9f60>] pstate: 600001c5
sp : ffffffc00070fbb0
x29: ffffffc00070fbb0 x28: ffffffc0fae77000
x27: 000000000000000c x26: 0000000000000003
x25: 00000000dffe0000 x24: 0000000000000000
x23: 0000000000000007 x22: ffffffc000768000
x21: ffffffc0f94a0884 x20: ffffffc000645b80
x19: ffffffc0f94a0800 x18: 0000007f863063e0
x17: 0000007f875d0280 x16: ffffffc0000f93ec
x15: 001b92d7f76c3f7d x14: 0000000000000000
x13: 00000003e8000000 x12: 0000000000000018
x11: 0000000000000000 x10: 0000000000000400
x9 : ffffffc00070fd20 x8 : 00000000fe871000
x7 : ffffffc0fa800038 x6 : ffffffc0fa800000
x5 : 00000000fffffffa x4 : 0000000000000000
x3 : 0000000080000000 x2 : 0000000000000001
x1 : ffffffc0fae7700c x0 : 0000000000000000

Process swapper/0 (pid: 0, stack limit = 0xffffffc00070c058)
Stack: (0xffffffc00070fbb0 to 0xffffffc000710000)
fba0:                                     0070fbc0 ffffffc0 002d7f84 ffffffc0
fbc0: 0070fbd0 ffffffc0 000e44f0 ffffffc0 0070fc00 ffffffc0 000e13e8 ffffffc0
fbe0: 00000002 00000000 fef7a900 ffffffc0 00709900 ffffffc0 000e13d4 ffffffc0
fc00: 0070fc20 ffffffc0 002da0ec ffffffc0 fac39000 ffffffc0 000d1e80 ffffffc0
fc20: 0070fca0 ffffffc0 002d74c4 ffffffc0 007096ec ffffffc0 fef7ef10 ffffffc0
fc40: 0064d878 ffffffc0 00775000 ffffffc0 00000000 00000000 00642500 ffffffc0
fc60: 006424f8 ffffffc0 00648318 ffffffc0 0070c000 ffffffc0 00000000 00000081
fc80: 00000000 00000000 a0000000 ffffffc0 00000000 00000000 002d7494 ffffffc0
fca0: 0070fcf0 ffffffc0 002d7574 ffffffc0 fac0c800 ffffffc0 0072cae0 ffffffc0
fcc0: fac26500 ffffffc0 00645b80 ffffffc0 00000018 00000000 fef79410 ffffffc0
fce0: 00000001 00000000 00648318 ffffffc0 0070fd00 ffffffc0 000a06a8 ffffffc0
fd00: 0070fd10 ffffffc0 000e50b0 ffffffc0 0070fd50 ffffffc0 000e13e8 ffffffc0
fd20: 00000018 00000000 00709000 ffffffc0 00642000 ffffffc0 00642000 ffffffc0
fd40: 00000018 00000000 00000000 00000000 0070fd70 ffffffc0 000848bc ffffffc0
fd60: 007095b0 ffffffc0 000848a4 ffffffc0 0070fdc0 ffffffc0 0008128c ffffffc0
fd80: 0076f000 ffffffc0 0000400c ffffff80 0070fdf0 ffffffc0 00004010 ffffff80
fda0: 60000145 00000000 00759cac ffffffc0 0070fdf0 ffffffc0 0070fdf0 ffffffc0
fdc0: 0070ff10 ffffffc0 00083dac ffffffc0 0070c000 ffffffc0 0070c000 ffffffc0
fde0: 0070ff10 ffffffc0 00084ef0 ffffffc0 00000000 00000000 00653708 ffffffc0
fe00: 00653708 ffffffc0 00000001 00000000 00000018 00000000 00000000 00000000
fe20: 00000001 00000000 00000400 00000000 00718db0 ffffffc0 0070fd20 ffffffc0
fe40: 00000400 00000000 00000000 00000000 00000018 00000000 e8000000 00000003
fe60: 00000000 00000000 f76c3f7d 001b92d7 000f93ec ffffffc0 875d0280 0000007f
fe80: 863063e0 0000007f 0070c000 ffffffc0 0070c000 ffffffc0 00761200 ffffffc0
fea0: 0051e000 ffffffc0 006424f8 ffffffc0 00759cac ffffffc0 00000001 00000000
fec0: 00648318 ffffffc0 0070c000 ffffffc0 00000000 00000081 0070ff10 ffffffc0
fee0: 00084eec ffffffc0 0070ff10 ffffffc0 00084ef0 ffffffc0 60000145 00000000
ff00: 0070c000 ffffffc0 0070c000 ffffffc0 0070ff20 ffffffc0 000d944c ffffffc0
ff20: 0070ff80 ffffffc0 00508944 ffffffc0 00768000 ffffffc0 0075b000 ffffffc0
ff40: 006fb9a0 ffffffc0 0075b000 ffffffc0 feffde40 ffffffc0 00000000 00000041
ff60: 0007b000 00000041 0007d000 00000041 00080450 ffffffc0 0050893c ffffffc0
ff80: 0070ffa0 ffffffc0 006d68a0 ffffffc0 00000002 00000000 0075b000 ffffffc0
ffa0: 00000000 00000000 00080210 00000041 00000000 00000000 00000e11 00000000
ffc0: 08000000 00000041 500f0000 00000000 0071a000 00000041 00000000 00000000
ffe0: 006fb9a0 ffffffc0 00000000 00000000 00000000 00000000 00000000 00000000
Call trace:
[<ffffffc000289304>] clear_bit+0x14/0x30
[<ffffffc0002d7f80>] ack_dynirq+0x20/0x2c
[<ffffffc0000e44ec>] handle_edge_irq+0x94/0x18c
[<ffffffc0000e13e4>] generic_handle_irq+0x24/0x40
[<ffffffc0002da0e8>] evtchn_fifo_handle_events+0x180/0x188
[<ffffffc0002d74c0>] __xen_evtchn_do_upcall+0x9c/0x144
[<ffffffc0002d7570>] xen_hvm_evtchn_do_upcall+0x8/0x14
[<ffffffc0000a06a4>] xen_arm_callback+0x8/0x18
[<ffffffc0000e50ac>] handle_percpu_devid_irq+0x90/0xb8
[<ffffffc0000e13e4>] generic_handle_irq+0x24/0x40
[<ffffffc0000848b8>] handle_IRQ+0x68/0xe0
[<ffffffc000081288>] gic_handle_irq+0x38/0x80
Exception stack(0xffffffc00070fdd0 to 0xffffffc00070fef0)
fdc0:                                     0070c000 ffffffc0 0070c000 ffffffc0
fde0: 0070ff10 ffffffc0 00084ef0 ffffffc0 00000000 00000000 00653708 ffffffc0
fe00: 00653708 ffffffc0 00000001 00000000 00000018 00000000 00000000 00000000
fe20: 00000001 00000000 00000400 00000000 00718db0 ffffffc0 0070fd20 ffffffc0
fe40: 00000400 00000000 00000000 00000000 00000018 00000000 e8000000 00000003
fe60: 00000000 00000000 f76c3f7d 001b92d7 000f93ec ffffffc0 875d0280 0000007f
fe80: 863063e0 0000007f 0070c000 ffffffc0 0070c000 ffffffc0 00761200 ffffffc0
fea0: 0051e000 ffffffc0 006424f8 ffffffc0 00759cac ffffffc0 00000001 00000000
fec0: 00648318 ffffffc0 0070c000 ffffffc0 00000000 00000081 0070ff10 ffffffc0
fee0: 00084eec ffffffc0 0070ff10 ffffffc0
[<ffffffc000083da8>] el1_irq+0x68/0xd8
[<ffffffc0000d9448>] cpu_startup_entry+0x114/0x174
[<ffffffc000508940>] rest_init+0x7c/0x88
[<ffffffc0006d689c>] start_kernel+0x350/0x368
Code: 4a030000 d2800022 8b400c21 9ac32043 (c85f7c22)


Thanks,
Pranav

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