Subject: Re: [PATCH kernel v3] powerpc/powernv: Isolate NVLinks between GV100GL on Witherspoon

From: Alex Williamson <[email-masked]>
Date: Tue, 30 Apr 2019 07:20:47 -0600

On Tue, 30 Apr 2019 16:14:35 +1000
Alexey Kardashevskiy <[email-masked]> wrote:

> On 30/04/2019 15:45, Alistair Popple wrote:
> > Alexey,
> >   
> >>>>> +void pnv_try_isolate_nvidia_v100(struct pci_dev *bridge)
> >>>>> +{
> >>>>> +	u32 mask, val;
> >>>>> +	void __iomem *bar0_0, *bar0_120000, *bar0_a00000;
> >>>>> +	struct pci_dev *pdev;
> >>>>> +	u16 cmd = 0, cmdmask = PCI_COMMAND_MEMORY;
> >>>>> +
> >>>>> +	if (!bridge->subordinate)
> >>>>> +		return;
> >>>>> +
> >>>>> +	pdev = list_first_entry_or_null(&bridge->subordinate->devices,
> >>>>> +			struct pci_dev, bus_list);
> >>>>> +	if (!pdev)
> >>>>> +		return;
> >>>>> +
> >>>>> +	if (pdev->vendor != PCI_VENDOR_ID_NVIDIA)  
> > 
> > Don't you also need to check the PCIe devid to match only [PV]100 devices as 
> > well? I doubt there's any guarantee these registers will remain the same for 
> > all future (or older) NVIDIA devices.  
> 
> 
> I do not have the complete list of IDs and I already saw 3 different
> device ids and this only works for machines with ibm,npu/gpu/nvlinks
> properties so for now it works and for the future we are hoping to
> either have an open source nvidia driver or some small minidriver (also
> from nvidia, or may be a spec allowing us to write one) to allow
> topology discovery on the host so we would not depend on the skiboot's
> powernv DT.
> 
> > IMHO this should really be done in the device driver in the guest. A malcious 
> > guest could load a modified driver that doesn't do this, but that should not 
> > compromise other guests which presumably load a non-compromised driver that 
> > disables the links on that guests GPU. However I guess in practice what you 
> > have here should work equally well.  
> 
> Doing it in the guest means a good guest needs to have an updated
> driver, we do not really want to depend on this. The idea of IOMMU
> groups is that the hypervisor provides isolation irrespective to what
> the guest does.

+1 It's not the user/guest driver's responsibility to maintain the
isolation of the device.  Thanks,

Alex

> Also vfio+qemu+slof needs to convey the nvlink topology to the guest,
> seems like an unnecessary complication.
> 
> 
> 
> > - Alistair
> >   
> >>>>> +		return;
> >>>>> +
> >>>>> +	mask = nvlinkgpu_get_disable_mask(&pdev->dev);
> >>>>> +	if (!mask)
> >>>>> +		return;
> >>>>> +
> >>>>> +	bar0_0 = pci_iomap_range(pdev, 0, 0, 0x10000);
> >>>>> +	if (!bar0_0) {
> >>>>> +		pci_err(pdev, "Error mapping BAR0 @0\n");
> >>>>> +		return;
> >>>>> +	}
> >>>>> +	bar0_120000 = pci_iomap_range(pdev, 0, 0x120000, 0x10000);
> >>>>> +	if (!bar0_120000) {
> >>>>> +		pci_err(pdev, "Error mapping BAR0 @120000\n");
> >>>>> +		goto bar0_0_unmap;
> >>>>> +	}
> >>>>> +	bar0_a00000 = pci_iomap_range(pdev, 0, 0xA00000, 0x10000);
> >>>>> +	if (!bar0_a00000) {
> >>>>> +		pci_err(pdev, "Error mapping BAR0 @A00000\n");
> >>>>> +		goto bar0_120000_unmap;
> >>>>> +	}  
> >>>>
> >>>> Is it really necessary to do three separate ioremaps vs one that would
> >>>> cover them all here?  I suspect you're just sneaking in PAGE_SIZE with
> >>>> the 0x10000 size mappings anyway.  Seems like it would simplify setup,
> >>>> error reporting, and cleanup to to ioremap to the PAGE_ALIGN'd range
> >>>> of the highest register accessed. Thanks,  
> >>>
> >>> Sure I can map it once, I just do not see the point in mapping/unmapping
> >>> all 0xa10000>>16=161 system pages for a very short period of time while
> >>> we know precisely that we need just 3 pages.
> >>>
> >>> Repost?  
> >>
> >> Ping?
> >>
> >> Can this go in as it is (i.e. should I ping Michael) or this needs
> >> another round? It would be nice to get some formal acks. Thanks,
> >>  
> >>>> Alex
> >>>>  
> >>>>> +
> >>>>> +	pci_restore_state(pdev);
> >>>>> +	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> >>>>> +	if ((cmd & cmdmask) != cmdmask)
> >>>>> +		pci_write_config_word(pdev, PCI_COMMAND, cmd | cmdmask);
> >>>>> +
> >>>>> +	/*
> >>>>> +	 * The sequence is from "Tesla P100 and V100 SXM2 NVLink Isolation on
> >>>>> +	 * Multi-Tenant Systems".
> >>>>> +	 * The register names are not provided there either, hence raw values.
> >>>>> +	 */
> >>>>> +	iowrite32(0x4, bar0_120000 + 0x4C);
> >>>>> +	iowrite32(0x2, bar0_120000 + 0x2204);
> >>>>> +	val = ioread32(bar0_0 + 0x200);
> >>>>> +	val |= 0x02000000;
> >>>>> +	iowrite32(val, bar0_0 + 0x200);
> >>>>> +	val = ioread32(bar0_a00000 + 0x148);
> >>>>> +	val |= mask;
> >>>>> +	iowrite32(val, bar0_a00000 + 0x148);
> >>>>> +
> >>>>> +	if ((cmd | cmdmask) != cmd)
> >>>>> +		pci_write_config_word(pdev, PCI_COMMAND, cmd);
> >>>>> +
> >>>>> +	pci_iounmap(pdev, bar0_a00000);
> >>>>> +bar0_120000_unmap:
> >>>>> +	pci_iounmap(pdev, bar0_120000);
> >>>>> +bar0_0_unmap:
> >>>>> +	pci_iounmap(pdev, bar0_0);
> >>>>> +}  
> > 
> >   
>