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

[Alistair Popple <alistair@popple.id.au>]

> 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?

- 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@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 = {
> >>>>>
> >>>>
> >>>>
> >>>
> >>>
> >>
> >>
> > 
> > 
> 
>