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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 16/10/2018 12:44, Alistair Popple wrote:
> Hi Alexey,
> 
> On Tuesday, 16 October 2018 12:37:49 PM AEDT Alexey Kardashevskiy wrote:
>>
>> On 16/10/2018 11:38, Alistair Popple wrote:
>>> Hi Alexey,
>>>
>>> Looking at the skiboot side I think we only fence the NVLink bricks as part of a
>>> PCIe function level reset (FLR) rather than a PCI Hot or Fundamental reset which
>>> I believe is what the code here does. So to fence the bricks you would need to
>>> do either a FLR on the given link or alter Skiboot to fence a given link as part
>>> of a hot reset.
>>
>> The code here calls OPAL to execute this code:
>>
>> https://github.com/open-power/skiboot/commit/fca2b2b839a673a1e52fc6b19ee6d33b2dfbc003
>>
>> This resets all links on an NPU which is fine for now as we pass GPUs in
>> groups only. Or I missed something?
> 
> From what I can see in
> https://github.com/open-power/skiboot/commit/2947eaa14e771e572d4e84bf003318c590c1c7d4
> we only fence the bricks in npu2_dev_procedure_reset()
> (https://github.com/open-power/skiboot/blob/master/hw/npu2-hw-procedures.c#L937)
> which itself is only called from the FLR path and not the code path you point
> out above.
> 
> The code path above only resets the NTL which I don't believe is sufficient to
> prevent HMIs.

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()?



> 
> - 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@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