Subject: Re: [PATCH kernel v5 20/20] vfio_pci: Add NVIDIA GV100GL [Tesla V100 SXM2] subdriver

From: Alex Williamson <[email-masked]>
Date: Tue, 18 Dec 2018 15:37:01 -0700

On Thu, 13 Dec 2018 17:17:34 +1100
Alexey Kardashevskiy <[email-masked]> wrote:

> POWER9 Witherspoon machines come with 4 or 6 V100 GPUs which are not
> pluggable PCIe devices but still have PCIe links which are used
> for config space and MMIO. In addition to that the GPUs have 6 NVLinks
> which are connected to other GPUs and the POWER9 CPU. POWER9 chips
> have a special unit on a die called an NPU which is an NVLink2 host bus
> adapter with p2p connections to 2 to 3 GPUs, 3 or 2 NVLinks to each.
> These systems also support ATS (address translation services) which is
> a part of the NVLink2 protocol. Such GPUs also share on-board RAM
> (16GB or 32GB) to the system via the same NVLink2 so a CPU has
> cache-coherent access to a GPU RAM.
> 
> This exports GPU RAM to the userspace as a new VFIO device region. This
> preregisters the new memory as device memory as it might be used for DMA.
> This inserts pfns from the fault handler as the GPU memory is not onlined
> until the vendor driver is loaded and trained the NVLinks so doing this
> earlier causes low level errors which we fence in the firmware so
> it does not hurt the host system but still better be avoided; for the same
> reason this does not map GPU RAM into the host kernel (usual thing for
> emulated access otherwise).
> 
> This exports an ATSD (Address Translation Shootdown) register of NPU which
> allows TLB invalidations inside GPU for an operating system. The register
> conveniently occupies a single 64k page. It is also presented to
> the userspace as a new VFIO device region. One NPU has 8 ATSD registers,
> each of them can be used for TLB invalidation in a GPU linked to this NPU.
> This allocates one ATSD register per an NVLink bridge allowing passing
> up to 6 registers. Due to the host firmware bug (just recently fixed),
> only 1 ATSD register per NPU was actually advertised to the host system
> so this passes that alone register via the first NVLink bridge device in
> the group which is still enough as QEMU collects them all back and
> presents to the guest via vPHB to mimic the emulated NPU PHB on the host.
> 
> In order to provide the userspace with the information about GPU-to-NVLink
> connections, this exports an additional capability called "tgt"
> (which is an abbreviated host system bus address). The "tgt" property
> tells the GPU its own system address and allows the guest driver to
> conglomerate the routing information so each GPU knows how to get directly
> to the other GPUs.
> 
> For ATS to work, the nest MMU (an NVIDIA block in a P9 CPU) needs to
> know LPID (a logical partition ID or a KVM guest hardware ID in other
> words) and PID (a memory context ID of a userspace process, not to be
> confused with a linux pid). This assigns a GPU to LPID in the NPU and
> this is why this adds a listener for KVM on an IOMMU group. A PID comes
> via NVLink from a GPU and NPU uses a PID wildcard to pass it through.
> 
> This requires coherent memory and ATSD to be available on the host as
> the GPU vendor only supports configurations with both features enabled
> and other configurations are known not to work. Because of this and
> because of the ways the features are advertised to the host system
> (which is a device tree with very platform specific properties),
> this requires enabled POWERNV platform.
> 
> The V100 GPUs do not advertise any of these capabilities via the config
> space and there are more than just one device ID so this relies on
> the platform to tell whether these GPUs have special abilities such as
> NVLinks.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> ---
> Changes:
> v5:
> * do not memremap GPU RAM for emulation, map it only when it is needed
> * allocate 1 ATSD register per NVLink bridge, if none left, then expose
> the region with a zero size
> * separate caps per device type
> * addressed AW review comments
> 
> v4:
> * added nvlink-speed to the NPU bridge capability as this turned out to
> be not a constant value
> * instead of looking at the exact device ID (which also changes from system
> to system), now this (indirectly) looks at the device tree to know
> if GPU and NPU support NVLink
> 
> v3:
> * reworded the commit log about tgt
> * added tracepoints (do we want them enabled for entire vfio-pci?)
> * added code comments
> * added write|mmap flags to the new regions
> * auto enabled VFIO_PCI_NVLINK2 config option
> * added 'tgt' capability to a GPU so QEMU can recreate ibm,npu and ibm,gpu
> references; there are required by the NVIDIA driver
> * keep notifier registered only for short time
> ---
>  drivers/vfio/pci/Makefile           |   1 +
>  drivers/vfio/pci/trace.h            | 102 ++++++
>  drivers/vfio/pci/vfio_pci_private.h |  14 +
>  include/uapi/linux/vfio.h           |  39 +++
>  drivers/vfio/pci/vfio_pci.c         |  27 +-
>  drivers/vfio/pci/vfio_pci_nvlink2.c | 473 ++++++++++++++++++++++++++++
>  drivers/vfio/pci/Kconfig            |   6 +
>  7 files changed, 660 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/vfio/pci/trace.h
>  create mode 100644 drivers/vfio/pci/vfio_pci_nvlink2.c
> 
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 76d8ec0..9662c06 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -1,5 +1,6 @@
>  
>  vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
>  vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
> +vfio-pci-$(CONFIG_VFIO_PCI_NVLINK2) += vfio_pci_nvlink2.o
>  
>  obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
> diff --git a/drivers/vfio/pci/trace.h b/drivers/vfio/pci/trace.h
> new file mode 100644
> index 0000000..b80d2d3
> --- /dev/null
> +++ b/drivers/vfio/pci/trace.h
> @@ -0,0 +1,102 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * VFIO PCI mmap/mmap_fault tracepoints
> + *
> + * Copyright (C) 2018 IBM Corp.  All rights reserved.
> + *     Author: Alexey Kardashevskiy <[email-masked]>
> + *
> + * 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.
> + */
> +
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM vfio_pci
> +
> +#if !defined(_TRACE_VFIO_PCI_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_VFIO_PCI_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(vfio_pci_nvgpu_mmap_fault,
> +	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
> +			vm_fault_t ret),
> +	TP_ARGS(pdev, hpa, ua, ret),
> +
> +	TP_STRUCT__entry(
> +		__field(const char *, name)
> +		__field(unsigned long, hpa)
> +		__field(unsigned long, ua)
> +		__field(int, ret)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->name = dev_name(&pdev->dev),
> +		__entry->hpa = hpa;
> +		__entry->ua = ua;
> +		__entry->ret = ret;
> +	),
> +
> +	TP_printk("%s: %lx -> %lx ret=%d", __entry->name, __entry->hpa,
> +			__entry->ua, __entry->ret)
> +);
> +
> +TRACE_EVENT(vfio_pci_nvgpu_mmap,
> +	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
> +			unsigned long size, int ret),
> +	TP_ARGS(pdev, hpa, ua, size, ret),
> +
> +	TP_STRUCT__entry(
> +		__field(const char *, name)
> +		__field(unsigned long, hpa)
> +		__field(unsigned long, ua)
> +		__field(unsigned long, size)
> +		__field(int, ret)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->name = dev_name(&pdev->dev),
> +		__entry->hpa = hpa;
> +		__entry->ua = ua;
> +		__entry->size = size;
> +		__entry->ret = ret;
> +	),
> +
> +	TP_printk("%s: %lx -> %lx size=%lx ret=%d", __entry->name, __entry->hpa,
> +			__entry->ua, __entry->size, __entry->ret)
> +);
> +
> +TRACE_EVENT(vfio_pci_npu2_mmap,
> +	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
> +			unsigned long size, int ret),
> +	TP_ARGS(pdev, hpa, ua, size, ret),
> +
> +	TP_STRUCT__entry(
> +		__field(const char *, name)
> +		__field(unsigned long, hpa)
> +		__field(unsigned long, ua)
> +		__field(unsigned long, size)
> +		__field(int, ret)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->name = dev_name(&pdev->dev),
> +		__entry->hpa = hpa;
> +		__entry->ua = ua;
> +		__entry->size = size;
> +		__entry->ret = ret;
> +	),
> +
> +	TP_printk("%s: %lx -> %lx size=%lx ret=%d", __entry->name, __entry->hpa,
> +			__entry->ua, __entry->size, __entry->ret)
> +);
> +
> +#endif /* _TRACE_SUBSYS_H */
> +
> +#undef TRACE_INCLUDE_PATH
> +#define TRACE_INCLUDE_PATH .
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_FILE trace
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 93c1738..127071b 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -163,4 +163,18 @@ static inline int vfio_pci_igd_init(struct vfio_pci_device *vdev)
>  	return -ENODEV;
>  }
>  #endif
> +#ifdef CONFIG_VFIO_PCI_NVLINK2
> +extern int vfio_pci_nvdia_v100_nvlink2_init(struct vfio_pci_device *vdev);
> +extern int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev);
> +#else
> +static inline int vfio_pci_nvdia_v100_nvlink2_init(struct vfio_pci_device *vdev)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev)
> +{
> +	return -ENODEV;
> +}
> +#endif
>  #endif /* VFIO_PCI_PRIVATE_H */
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 8131028..ce28d39 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -353,6 +353,21 @@ struct vfio_region_gfx_edid {
>  #define VFIO_DEVICE_GFX_LINK_STATE_DOWN  2
>  };
>  
> +/*
> + * 10de vendor sub-type
> + *
> + * NVIDIA GPU NVlink2 RAM is coherent RAM mapped onto the host address space.
> + */
> +#define VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM	(1)
> +
> +/*
> + * 1014 vendor sub-type
> + *
> + * IBM NPU NVlink2 ATSD (Address Translation Shootdown) register of NPU
> + * to do TLB invalidation on a GPU.
> + */
> +#define VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD	(1)
> +
>  /*
>   * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
>   * which allows direct access to non-MSIX registers which happened to be within
> @@ -363,6 +378,30 @@ struct vfio_region_gfx_edid {
>   */
>  #define VFIO_REGION_INFO_CAP_MSIX_MAPPABLE	3
>  
> +/*
> + * Capability with compressed real address (aka SSA - small system address)
> + * where GPU RAM is mapped on a system bus. Used by a GPU for DMA routing.
> + */
> +#define VFIO_REGION_INFO_CAP_NVIDIA_NVLINK2	4
> +
> +struct vfio_region_info_cap_nvidia_nvlink2 {
> +	struct vfio_info_cap_header header;
> +	__u64 tgt;
> +};
> +
> +/*
> + * Capability with compressed real address (aka SSA - small system address),
> + * used to match the NVLink bridge with a GPU. Also contains a link speed.
> + */
> +#define VFIO_REGION_INFO_CAP_IBM_NPU2		5
> +
> +struct vfio_region_info_cap_ibm_npu2 {
> +	struct vfio_info_cap_header header;
> +	__u64 tgt;
> +	__u32 link_speed;
> +	__u32 __pad;
> +};

Another option here would be to have one capability expose tgt used by
both devices and another capability expose link_speed used only by the
NPU.  Perhaps VFIO_REGION_INFO_CAP_NVLINK2_SSATGT and
VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD.  We don't necessarily need to make
each capability specific to a device and we can stack multiple
together.  Is there some association between tgt and link_speed that
requires them together?  We could also simply expose the link_speed as
a __u64 rather than introduce padding.  Thanks,

Alex