Re: [PATCH] perf/x86/intel/cqm: Check cqm/mbm enabled state in event init

[Peter Zijlstra]

On Mon, Sep 05, 2016 at 05:30:07PM +0200, Jiri Olsa wrote:
> Yanqiu Zhang reported kernel panic when using mbm event
> on system where CQM is detected but without mbm event
> support, like with perf:
> 
>   # perf stat -e 'intel_cqm/event=3/' -a
> 
>   BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
>   IP: [<ffffffff8100d64c>] update_sample+0xbc/0xe0
>   ...
>    <IRQ>
>    [<ffffffff8100d688>] __intel_mbm_event_init+0x18/0x20
>    [<ffffffff81113d6b>] flush_smp_call_function_queue+0x7b/0x160
>    [<ffffffff81114853>] generic_smp_call_function_single_interrupt+0x13/0x60
>    [<ffffffff81052017>] smp_call_function_interrupt+0x27/0x40
>    [<ffffffff816fb06c>] call_function_interrupt+0x8c/0xa0
>   ...
> 
> The reason is that we currently allow to init mbm event
> even if mbm support is not detected.  Adding checks for
> both cqm and mbm events and support into cqm's event_init.
> 
> Reported-by: Yanqiu Zhang <yanqzhan@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>

Fixes: 33c3cc7acfd9 ("perf/x86/mbm: Add Intel Memory B/W Monitoring enumeration and init")

Cc: stable@xxxxxxxxxxxxxxxx # 4.6+