linux-kernel - Re: [PATCH] drm/amdkfd: Remove vla

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Date:   Tue, 10 Apr 2018 11:43:57 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Christian König <christian.koenig@....com>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] drm/amdkfd: Remove vla

On 04/09/2018 11:38 PM, Christian König wrote:
> Am 09.04.2018 um 23:06 schrieb Laura Abbott:
>> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
>> turn on -Wvla. The single VLA usage in the amdkfd driver is actually
>> constant across all current platforms.
> 
> Actually that isn't correct.
> 
> Could be that we haven't upstreamed KFD support for them, but Vega10 have a different interrupt ring entry size and so would cause the error message here.
> 
>> Switch to a constant size array
>> instead.
> 
> I would say to just make make the array bigger.
> 
> Regards,
> Christian.
> 

What array size would accommodate future chips?

>>
>> [1] https://lkml.org/lkml/2018/3/7/621
>>
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>>   drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
>> index 035c351f47c5..c9863858f343 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
>> @@ -139,10 +139,12 @@ static void interrupt_wq(struct work_struct *work)
>>   {
>>       struct kfd_dev *dev = container_of(work, struct kfd_dev,
>>                           interrupt_work);
>> +    uint32_t ih_ring_entry[4];
>> -    uint32_t ih_ring_entry[DIV_ROUND_UP(
>> -                dev->device_info->ih_ring_entry_size,
>> -                sizeof(uint32_t))];
>> +    if (dev->device_info->ih_ring_entry_size > (4 * sizeof(uint32_t))) {
>> +        dev_err(kfd_chardev(), "Ring entry too small\n");
>> +        return;
>> +    }
>>       while (dequeue_ih_ring_entry(dev, ih_ring_entry))
>>           dev->device_info->event_interrupt_class->interrupt_wq(dev,
>