Re: [RFC PATCH kernel v2] powerpc/powernv: Isolate NVLinks between GV100GL on Witherspoon

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On Thu,  4 Apr 2019 16:23:24 +1100
Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:

> The NVIDIA V100 SXM2 GPUs are connected to the CPU via PCIe links and
> (on POWER9) NVLinks. In addition to that, GPUs themselves have direct
> peer to peer NVLinks in groups of 2 to 4 GPUs. At the moment the POWERNV
> platform puts all interconnected GPUs to the same IOMMU group.
> 
> However the user may want to pass individual GPUs to the userspace so
> in order to do so we need to put them into separate IOMMU groups and
> cut off the interconnects.
> 
> Thankfully V100 GPUs implement an interface to do by programming link
> disabling mask to BAR0 of a GPU. Once a link is disabled in a GPU using
> this interface, it cannot be re-enabled until the secondary bus reset is
> issued to the GPU.
> 
> This adds an extra step to the secondary bus reset handler (the one used
> for such GPUs) to block NVLinks to GPUs which do not belong to the same
> group as the GPU being reset.
> 
> This adds a new "isolate_nvlink" kernel parameter to allow GPU isolation;
> when enabled, every GPU gets its own IOMMU group. The new parameter is off
> by default to preserve the existing behaviour.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> ---
> Changes:
> v2:
> * this is rework of [PATCH kernel RFC 0/2] vfio, powerpc/powernv: Isolate GV100GL
> but this time it is contained in the powernv platform
> ---
>  arch/powerpc/platforms/powernv/Makefile      |   2 +-
>  arch/powerpc/platforms/powernv/pci.h         |   1 +
>  arch/powerpc/platforms/powernv/eeh-powernv.c |   1 +
>  arch/powerpc/platforms/powernv/npu-dma.c     |  24 +++-
>  arch/powerpc/platforms/powernv/nvlinkgpu.c   | 131 +++++++++++++++++++
>  5 files changed, 156 insertions(+), 3 deletions(-)
>  create mode 100644 arch/powerpc/platforms/powernv/nvlinkgpu.c
> 
> diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
> index da2e99efbd04..60a10d3b36eb 100644
> --- a/arch/powerpc/platforms/powernv/Makefile
> +++ b/arch/powerpc/platforms/powernv/Makefile
> @@ -6,7 +6,7 @@ obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
>  obj-y			+= opal-kmsg.o opal-powercap.o opal-psr.o opal-sensor-groups.o
>  
>  obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
> -obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-ioda-tce.o
> +obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-ioda-tce.o nvlinkgpu.o
>  obj-$(CONFIG_CXL_BASE)	+= pci-cxl.o
>  obj-$(CONFIG_EEH)	+= eeh-powernv.o
>  obj-$(CONFIG_PPC_SCOM)	+= opal-xscom.o
> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
> index 8e36da379252..9fd3f391482c 100644
> --- a/arch/powerpc/platforms/powernv/pci.h
> +++ b/arch/powerpc/platforms/powernv/pci.h
> @@ -250,5 +250,6 @@ extern void pnv_pci_unlink_table_and_group(struct iommu_table *tbl,
>  extern void pnv_pci_setup_iommu_table(struct iommu_table *tbl,
>  		void *tce_mem, u64 tce_size,
>  		u64 dma_offset, unsigned int page_shift);
> +extern void pnv_try_isolate_nvidia_v100(struct pci_dev *gpdev);
>  
>  #endif /* __POWERNV_PCI_H */
> diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
> index f38078976c5d..464b097d9635 100644
> --- a/arch/powerpc/platforms/powernv/eeh-powernv.c
> +++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
> @@ -937,6 +937,7 @@ void pnv_pci_reset_secondary_bus(struct pci_dev *dev)
>  		pnv_eeh_bridge_reset(dev, EEH_RESET_HOT);
>  		pnv_eeh_bridge_reset(dev, EEH_RESET_DEACTIVATE);
>  	}
> +	pnv_try_isolate_nvidia_v100(dev);
>  }
>  
>  static void pnv_eeh_wait_for_pending(struct pci_dn *pdn, const char *type,
> diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> index dc23d9d2a7d9..017eae8197e7 100644
> --- a/arch/powerpc/platforms/powernv/npu-dma.c
> +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> @@ -529,6 +529,23 @@ static void pnv_comp_attach_table_group(struct npu_comp *npucomp,
>  	++npucomp->pe_num;
>  }
>  
> +static bool isolate_nvlink;
> +
> +static int __init parse_isolate_nvlink(char *p)
> +{
> +	bool val;
> +
> +	if (!p)
> +		val = true;
> +	else if (kstrtobool(p, &val))
> +		return -EINVAL;
> +
> +	isolate_nvlink = val;
> +
> +	return 0;
> +}
> +early_param("isolate_nvlink", parse_isolate_nvlink);
> +
>  struct iommu_table_group *pnv_try_setup_npu_table_group(struct pnv_ioda_pe *pe)
>  {
>  	struct iommu_table_group *table_group;
> @@ -549,7 +566,7 @@ struct iommu_table_group *pnv_try_setup_npu_table_group(struct pnv_ioda_pe *pe)
>  
>  	hose = pci_bus_to_host(npdev->bus);
>  
> -	if (hose->npu) {
> +	if (hose->npu && !isolate_nvlink) {
>  		table_group = &hose->npu->npucomp.table_group;
>  
>  		if (!table_group->group) {
> @@ -559,7 +576,10 @@ struct iommu_table_group *pnv_try_setup_npu_table_group(struct pnv_ioda_pe *pe)
>  					pe->pe_number);
>  		}
>  	} else {
> -		/* Create a group for 1 GPU and attached NPUs for POWER8 */
> +		/*
> +		 * Create a group for 1 GPU and attached NPUs for
> +		 * POWER8 (always) or POWER9 (when isolate_nvlink).
> +		 */
>  		pe->npucomp = kzalloc(sizeof(*pe->npucomp), GFP_KERNEL);
>  		table_group = &pe->npucomp->table_group;
>  		table_group->ops = &pnv_npu_peers_ops;
> diff --git a/arch/powerpc/platforms/powernv/nvlinkgpu.c b/arch/powerpc/platforms/powernv/nvlinkgpu.c
> new file mode 100644
> index 000000000000..dbd8e9d47a05
> --- /dev/null
> +++ b/arch/powerpc/platforms/powernv/nvlinkgpu.c
> @@ -0,0 +1,131 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * A helper to disable NVLinks between GPUs on IBM Withersponn platform.
> + *
> + * Copyright (C) 2019 IBM Corp.  All rights reserved.
> + *     Author: Alexey Kardashevskiy <aik@xxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/of.h>
> +#include <linux/iommu.h>
> +#include <linux/pci.h>
> +
> +static int nvlinkgpu_is_ph_in_group(struct device *dev, void *data)
> +{
> +	return dev->of_node->phandle == *(phandle *) data;
> +}
> +
> +static u32 nvlinkgpu_get_disable_mask(struct device *dev)
> +{
> +	int npu, peer;
> +	u32 mask;
> +	struct device_node *dn;
> +	struct iommu_group *group;
> +
> +	dn = dev->of_node;
> +	if (!of_find_property(dn, "ibm,nvlink-peers", NULL))
> +		return 0;
> +
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		return 0;
> +
> +	/*
> +	 * Collect links to keep which includes links to NPU and links to
> +	 * other GPUs in the same IOMMU group.
> +	 */
> +	for (npu = 0, mask = 0; ; ++npu) {
> +		u32 npuph = 0;
> +
> +		if (of_property_read_u32_index(dn, "ibm,npu", npu, &npuph))
> +			break;
> +
> +		for (peer = 0; ; ++peer) {
> +			u32 peerph = 0;
> +
> +			if (of_property_read_u32_index(dn, "ibm,nvlink-peers",
> +					peer, &peerph))
> +				break;
> +
> +			if (peerph != npuph &&
> +				!iommu_group_for_each_dev(group, &peerph,
> +					nvlinkgpu_is_ph_in_group))
> +				continue;
> +
> +			mask |= 1 << (peer + 16);
> +		}
> +	}
> +	iommu_group_put(group);
> +
> +	/* Disabling mechanism takes links to disable so invert it here */
> +	mask = ~mask & 0x3F0000;
> +
> +	return mask;
> +}
> +
> +void pnv_try_isolate_nvidia_v100(struct pci_dev *bridge)
> +{
> +	u32 mask;
> +	void __iomem *bar0_0, *bar0_120000, *bar0_a00000;
> +	struct pci_dev *pdev;
> +
> +	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)
> +		return;
> +
> +	mask = nvlinkgpu_get_disable_mask(&pdev->dev);
> +	if (!mask)
> +		return;
> +
> +	bar0_0 = pci_iomap_range(pdev, 0, 0, 0x10000);
> +	bar0_120000 = pci_iomap_range(pdev, 0, 0x120000, 0x10000);
> +	bar0_a00000 = pci_iomap_range(pdev, 0, 0xA00000, 0x10000);
> +
> +	if (bar0_120000 && bar0_0 && bar0_a00000) {
> +		u32 val;
> +		u16 cmd = 0, cmdmask = PCI_COMMAND_MEMORY;
> +
> +		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);
> +	}
> +


It's a little troubling that if something goes wrong with an iomap
we'll silently fail to re-enable the expected isolation.  Seems worthy
of at least a pci_warn/err.  Thanks,

Alex

> +	if (bar0_0)
> +		pci_iounmap(pdev, bar0_0);
> +	if (bar0_120000)
> +		pci_iounmap(pdev, bar0_120000);
> +	if (bar0_a00000)
> +		pci_iounmap(pdev, bar0_a00000);
> +}




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