Re: [PATCH] arm64/numa: Add more vetting in numa_set_distance()

[John Garry <john.garry@huawei.com>]

On 29/10/2018 12:16, Will Deacon wrote:
> On Mon, Oct 29, 2018 at 12:14:09PM +0000, John Garry wrote:
>> On 29/10/2018 11:25, Will Deacon wrote:
>>> On Fri, Oct 26, 2018 at 09:57:47PM +0800, John Garry wrote:
>>>> Currently it is acceptable to set the distance between 2 separate nodes to
>>>> LOCAL_DISTANCE.
>>>>
>>>> Reject this as it is invalid.
>>>>
>>>> This change avoids a crash reported in [1].
>>>>
>>>> [1] https://www.spinics.net/lists/arm-kernel/msg683304.html
>>>>
>>>> Signed-off-by: John Garry <john.garry@huawei.com>
>>>>
>>>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>>>> index 146c04c..6092e3d 100644
>>>> --- a/arch/arm64/mm/numa.c
>>>> +++ b/arch/arm64/mm/numa.c
>>>> @@ -335,7 +335,8 @@ void __init numa_set_distance(int from, int to, int distance)
>>>> 	}
>>>>
>>>> 	if ((u8)distance != distance ||
>>>> -	    (from == to && distance != LOCAL_DISTANCE)) {
>>>> +	    (from == to && distance != LOCAL_DISTANCE) ||
>>>> +	    (from != to && distance == LOCAL_DISTANCE)) {
>>>
>>> The current code here is more-or-less lifted from the x86 implementation
>>> of numa_set_distance().
>>
>> Right, I did notice this. I didn't think that x86 folks would be so
>> concerned since they generally only use ACPI, and the ACPI code already
>> validates these distances in drivers/acpi/numa.c: slit_valid() [unlike OF
>> code].
>>
>>  I think we should either factor out the sanity check
>>> into a core helper or make the core code robust to these funny configurations.
>>
>> OK, so to me it would make sense to factor out a sanity check into a core
>> helper.
>
> That, or have the OF code perform the same validation that slit_valid() is
> doing for ACPI. I'm just trying to avoid other architectures running into
> this problem down the line.
>

Right, OF code should do this validation job if ACPI is doing it 
(especially since the DT bindings actually specify the distance rules), 
and not rely on the arch NUMA code to accept/reject numa_set_distance() 
combinations.

And, in addition to this, I'd say OF should disable NUMA if given an 
invalid table (like ACPI does).

Cheers,
John

> Will
>
> .
>