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

On 16/10/2018 13:19, Alistair Popple wrote:

quoted

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 ;)

- Alistair

quoted

quoted

- Alistair

quoted

quoted

- Alistair

On Monday, 15 October 2018 6:17:51 PM AEDT Alexey Kardashevskiy wrote:

quoted

Ping?


On 02/10/2018 13:20, Alexey Kardashevskiy wrote:

quoted

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 <redacted>
---
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