[PATCH kernel v2] powerpc/ioda/npu: Call skiboot's hot reset hook when disabling NPU2

[Alexey Kardashevskiy]

On 16/10/2018 18:32, Alistair Popple wrote:
> On Tuesday, 16 October 2018 1:22:53 PM AEDT Alexey Kardashevskiy wrote:
>>
>> On 16/10/2018 13:19, Alistair Popple wrote:
>>>> reset_ntl() does what npu2_dev_procedure_reset() does plus more stuff,
>>>> there nothing really in npu2_dev_procedure_reset() which reset_ntl()
>>>> does not do already from the hardware standpoint. And it did stop HMIs
>>>> for me though.
>>>>
>>>> but ok, what will be sufficient then if not reset_ntl()?
>>>
>>> Argh, yes you are correct. Specifically both npu2_dev_procedure_reset() and
>>> reset_ntl() contain:
>>>
>>> 	/* NTL Reset */
>>> 	val = npu2_read(ndev->npu, NPU2_NTL_MISC_CFG1(ndev));
>>> 	val |= PPC_BIT(8) | PPC_BIT(9);
>>> 	npu2_write(ndev->npu, NPU2_NTL_MISC_CFG1(ndev), val);
>>>
>>> Which should fence the brick. However from what I recall there was more to
>>> reliably preventing HMIs than merely fencing the brick. It invovled a sequence
>>> of fencing and flushing the cache with dcbf instructions at the right time which
>>> is why we also have the FLR. Unfortunately I don't know the precise details,
>>> perhaps if we send enough coffee Balbir's way he might be able remind us?
>>
>>
>> He suggested and ack'ed that skiboot patch, I can repeat beers^wcoffee
>> but it won't change much ;)
> 
> Ha. Couldn't hurt ;)
> 
> I was pretty sure flushing the caches was an important part of the sequence to
> avoid HMI's. I believe you are trying to deal with unexpected guest terminations
> which means the driver won't have a chance to flush the caches prior to
> termination so

Correct.

> wouldn't you also need to do that somewhere? Unless the driver
> does it at startup?


VFIO performs GPU reset so I'd expect the GPUs to flush its caches
without any software interactions. Am I hoping for too much here?




> 
> - Alistair
> 
>>>
>>> - Alistair
>>>
>>>>
>>>>
>>>>>
>>>>> - Alistair
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> - Alistair
>>>>>>>
>>>>>>> On Monday, 15 October 2018 6:17:51 PM AEDT Alexey Kardashevskiy wrote:
>>>>>>>> Ping?
>>>>>>>>
>>>>>>>>
>>>>>>>> On 02/10/2018 13:20, Alexey Kardashevskiy wrote:
>>>>>>>>> The skiboot firmware has a hot reset handler which fences the NVIDIA V100
>>>>>>>>> GPU RAM on Witherspoons and makes accesses no-op instead of throwing HMIs:
>>>>>>>>> https://github.com/open-power/skiboot/commit/fca2b2b839a67
>>>>>>>>>
>>>>>>>>> Now we are going to pass V100 via VFIO which most certainly involves
>>>>>>>>> KVM guests which are often terminated without getting a chance to offline
>>>>>>>>> GPU RAM so we end up with a running machine with misconfigured memory.
>>>>>>>>> Accessing this memory produces hardware management interrupts (HMI)
>>>>>>>>> which bring the host down.
>>>>>>>>>
>>>>>>>>> To suppress HMIs, this wires up this hot reset hook to vfio_pci_disable()
>>>>>>>>> via pci_disable_device() which switches NPU2 to a safe mode and prevents
>>>>>>>>> HMIs.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>>>>>>>>> ---
>>>>>>>>> Changes:
>>>>>>>>> v2:
>>>>>>>>> * updated the commit log
>>>>>>>>> ---
>>>>>>>>>  arch/powerpc/platforms/powernv/pci-ioda.c | 10 ++++++++++
>>>>>>>>>  1 file changed, 10 insertions(+)
>>>>>>>>>
>>>>>>>>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>>>>> index cde7102..e37b9cc 100644
>>>>>>>>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>>>>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>>>>> @@ -3688,6 +3688,15 @@ static void pnv_pci_release_device(struct pci_dev *pdev)
>>>>>>>>>  		pnv_ioda_release_pe(pe);
>>>>>>>>>  }
>>>>>>>>>  
>>>>>>>>> +static void pnv_npu_disable_device(struct pci_dev *pdev)
>>>>>>>>> +{
>>>>>>>>> +	struct eeh_dev *edev = pci_dev_to_eeh_dev(pdev);
>>>>>>>>> +	struct eeh_pe *eehpe = edev ? edev->pe : NULL;
>>>>>>>>> +
>>>>>>>>> +	if (eehpe && eeh_ops && eeh_ops->reset)
>>>>>>>>> +		eeh_ops->reset(eehpe, EEH_RESET_HOT);
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>>  static void pnv_pci_ioda_shutdown(struct pci_controller *hose)
>>>>>>>>>  {
>>>>>>>>>  	struct pnv_phb *phb = hose->private_data;
>>>>>>>>> @@ -3732,6 +3741,7 @@ static const struct pci_controller_ops pnv_npu_ioda_controller_ops = {
>>>>>>>>>  	.reset_secondary_bus	= pnv_pci_reset_secondary_bus,
>>>>>>>>>  	.dma_set_mask		= pnv_npu_dma_set_mask,
>>>>>>>>>  	.shutdown		= pnv_pci_ioda_shutdown,
>>>>>>>>> +	.disable_device		= pnv_npu_disable_device,
>>>>>>>>>  };
>>>>>>>>>  
>>>>>>>>>  static const struct pci_controller_ops pnv_npu_ocapi_ioda_controller_ops = {
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
> 
> 

-- 
Alexey