Message-ID: <20231218151717.169f80aa.alex.williamson@redhat.com>
Date: Mon, 18 Dec 2023 15:17:17 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: <ankita@...dia.com>
Cc: <jgg@...dia.com>, <yishaih@...dia.com>,
 <shameerali.kolothum.thodi@...wei.com>, <kevin.tian@...el.com>,
 <eric.auger@...hat.com>, <brett.creeley@....com>, <horms@...nel.org>,
 <aniketa@...dia.com>, <cjia@...dia.com>, <kwankhede@...dia.com>,
 <targupta@...dia.com>, <vsethi@...dia.com>, <acurrid@...dia.com>,
 <apopple@...dia.com>, <jhubbard@...dia.com>, <danw@...dia.com>,
 <anuaggarwal@...dia.com>, <mochs@...dia.com>, <kvm@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v15 1/1] vfio/nvgrace-gpu: Add vfio pci variant module
 for grace hopper

On Mon, 18 Dec 2023 00:40:31 +0530
<ankita@...dia.com> wrote:

> From: Ankit Agrawal <ankita@...dia.com>
> 
> NVIDIA's upcoming Grace Hopper Superchip provides a PCI-like device
> for the on-chip GPU that is the logical OS representation of the
> internal proprietary chip-to-chip cache coherent interconnect.
> 
> The device is peculiar compared to a real PCI device in that whilst
> there is a real 64b PCI BAR1 (comprising region 2 & region 3) on the
> device, it is not used to access device memory once the faster
> chip-to-chip interconnect is initialized (occurs at the time of host
> system boot). The device memory is accessed instead using the chip-to-chip
> interconnect that is exposed as a contiguous physically addressable
> region on the host. This device memory aperture can be obtained from host
> ACPI table using device_property_read_u64(), according to the FW
> specification. Since the device memory is cache coherent with the CPU,
> it can be mmap into the user VMA with a cacheable mapping using
> remap_pfn_range() and used like a regular RAM. The device memory
> is not added to the host kernel, but mapped directly as this reduces
> memory wastage due to struct pages.
> 
> There is also a requirement of a reserved 1G uncached region (termed as
> resmem) to support the Multi-Instance GPU (MIG) feature [1]. Based on [2],
> the requisite properties (uncached, unaligned access) can be achieved
> through a VM mapping (S1) of NORMAL_NC and host (S2) mapping with
> MemAttr[2:0]=0b101. To provide a different non-cached property to the
> reserved 1G region, it needs to be carved out from the device memory and
> mapped as a separate region in Qemu VMA with pgprot_writecombine().
> pgprot_writecombine() sets the Qemu VMA page properties (pgprot) as
> NORMAL_NC.
> 
> Provide a VFIO PCI variant driver that adapts the unique device memory
> representation into a more standard PCI representation facing userspace.
> 
> The variant driver exposes these two regions - the non-cached reserved
> (resmem) and the cached rest of the device memory (termed as usemem) as
> separate VFIO 64b BAR regions. Since the device implements 64-bit BAR0,
> the VFIO PCI variant driver maps the uncached carved out region to the
> next available PCI BAR (i.e. comprising of region 2 and 3). The cached
> device memory aperture is assigned BAR region 4 and 5. Qemu will then
> naturally generate a PCI device in the VM with the uncached aperture
> reported as BAR2 region, the cacheable as BAR4. The variant driver provides
> emulation for these fake BARs' PCI config space offset registers. The
> BAR can also be enabled/disabled through PCI_COMMAND config space register.
> The VM driver should enable the BARs (as it does already) to make use
> of the device memory.
> 
> The memory layout on the host looks like the following:
>                devmem (memlength)
> |--------------------------------------------------|
> |-------------cached------------------------|--NC--|
> |                                           |
> usemem.phys/memphys                         resmem.phys
> 
> PCI BARs need to be aligned to the power-of-2, but the actual memory on the
> device may not. A read or write access to the physical address from the
> last device PFN up to the next power-of-2 aligned physical address
> results in reading ~0 and dropped writes. Note that the GPU device
> driver [6] is capable of knowing the exact device memory size through
> separate means. The device memory size is primarily kept in the system
> ACPI tables for use by the VFIO PCI variant module.
> 
> Note that the usemem memory is added by the VM Nvidia device driver [5]
> to the VM kernel as memblocks. Hence make the usable memory size memblock
> aligned.
> 
> Currently there is no provision in KVM for a S2 mapping with
> MemAttr[2:0]=0b101, but there is an ongoing effort to provide the same [3].
> As previously mentioned, resmem is mapped pgprot_writecombine(), that
> sets the Qemu VMA page properties (pgprot) as NORMAL_NC. Using the
> proposed changes in [4] and [3], KVM marks the region with
> MemAttr[2:0]=0b101 in S2.
> 
> This goes along with a qemu series [6] to provides the necessary
> implementation of the Grace Hopper Superchip firmware specification so
> that the guest operating system can see the correct ACPI modeling for
> the coherent GPU device. Verified with the CUDA workload in the VM.
> 
> [1] https://www.nvidia.com/en-in/technologies/multi-instance-gpu/
> [2] section D8.5.5 of https://developer.arm.com/documentation/ddi0487/latest/
> [3] https://lore.kernel.org/all/20231205033015.10044-1-ankita@nvidia.com/
> [4] https://lore.kernel.org/all/20230907181459.18145-2-ankita@nvidia.com/
> [5] https://github.com/NVIDIA/open-gpu-kernel-modules
> [6] https://lore.kernel.org/all/20231203060245.31593-1-ankita@nvidia.com/
> 
> Applied over next-20231211.
> ---
> Link for variant driver v14:
> https://lore.kernel.org/all/20231212184613.3237-1-ankita@nvidia.com/
> 
> v14 -> v15
> - Added case to handle VFIO_DEVICE_IOEVENTFD to return -EIO as it
>   is not required on the device.
> - Updated the BAR config space handling code to closely resemble
>   by Yishai Hadas (using range_intersect_range) in
>   https://lore.kernel.org/all/20231207102820.74820-10-yishaih@nvidia.com
> - Changed the bar pci config register from union to u64.
> - Adapted the code to disable BAR when it is disabled through
>   PCI_COMMAND.
> - Exported and reused the do_io_rw to do mmio accesses.
> - Added a new header file to keep the newly declared structures.
> - Miscellaneous code fixes suggested by Alex Williamson in v14.
> 
> v13 -> v14
> - Merged the changes for second BAR implementation for MIG support
>   on the device driver.
>   https://lore.kernel.org/all/20231115080751.4558-1-ankita@nvidia.com/
> - Added the missing implementation of sub-word access to fake BARs'
>   PCI config access. Implemented access algorithm suggested by
>   Alex Williamson in the comments (Thanks!)
> - Added support to BAR accesses on the reserved memory with
>   Qemu device param x-no-mmap=on.
> - Handled endian-ness in the PCI config space access.
> - Git commit message change
> 
> v12 -> v13
> - Added emulation for the PCI config space BAR offset register for
> the fake BAR.
> - commit message updated with more details on the BAR offset emulation.
> 
> v11 -> v12
> - More details in commit message on device memory size
> 
> v10 -> v11
> - Removed sysfs attribute to expose the CPU coherent memory feature
> - Addressed review comments
> 
> v9 -> v10
> - Add new sysfs attribute to expose the CPU coherent memory feature.
> 
> v8 -> v9
> - Minor code adjustment suggested in v8.
> 
> v7 -> v8
> - Various field names updated.
> - Added a new function to handle VFIO_DEVICE_GET_REGION_INFO ioctl.
> - Locking protection for memremap to bar region and other changes
>   recommended in v7.
> - Added code to fail if the devmem size advertized is 0 in system DSDT.
> 
> v6 -> v7
> - Handled out-of-bound and overflow conditions at various places to validate
>   input offset and length.
> - Added code to return EINVAL for offset beyond region size.
> 
> v5 -> v6
> - Added the code to handle BAR2 read/write using memremap to the device
>   memory.
> 
> v4 -> v5
> - Changed the module name from nvgpu-vfio-pci to nvgrace-gpu-vfio-pci.
> - Fixed memory leak and added suggested boundary checks on device memory
>   mapping.
> - Added code to read all Fs and ignored write on region outside of the
>   physical memory.
> - Other miscellaneous cleanup suggestions.
> 
> v3 -> v4
> - Mapping the available device memory using sparse mmap. The region outside
>   the device memory is handled by read/write ops.
> - Removed the fault handler added in v3.
> 
> v2 -> v3
> - Added fault handler to map the region outside the physical GPU memory
>   up to the next power-of-2 to a dummy PFN.
> - Changed to select instead of "depends on" VFIO_PCI_CORE for all the
>   vfio-pci variant driver.
> - Code cleanup based on feedback comments.
> - Code implemented and tested against v6.4-rc4.
> 
> v1 -> v2
> - Updated the wording of reference to BAR offset and replaced with
>   index.
> - The GPU memory is exposed at the fixed BAR2_REGION_INDEX.
> - Code cleanup based on feedback comments.
> 
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> Signed-off-by: Aniket Agashe <aniketa@...dia.com>
> Tested-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  MAINTAINERS                           |   6 +
>  drivers/vfio/pci/Kconfig              |   2 +
>  drivers/vfio/pci/Makefile             |   2 +
>  drivers/vfio/pci/nvgrace-gpu/Kconfig  |  10 +
>  drivers/vfio/pci/nvgrace-gpu/Makefile |   3 +
>  drivers/vfio/pci/nvgrace-gpu/main.c   | 806 ++++++++++++++++++++++++++
>  drivers/vfio/pci/vfio_pci_rdwr.c      |   9 +-
>  7 files changed, 834 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/vfio/pci/nvgrace-gpu/Kconfig
>  create mode 100644 drivers/vfio/pci/nvgrace-gpu/Makefile
>  create mode 100644 drivers/vfio/pci/nvgrace-gpu/main.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 98f7dd0499f1..6f8f3a6daa43 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -22877,6 +22877,12 @@ L:	kvm@...r.kernel.org
>  S:	Maintained
>  F:	drivers/vfio/platform/
>  
> +VFIO NVIDIA GRACE GPU DRIVER
> +M:	Ankit Agrawal <ankita@...dia.com>
> +L:	kvm@...r.kernel.org
> +S:	Maintained
> +F:	drivers/vfio/pci/nvgrace-gpu/
> +
>  VGA_SWITCHEROO
>  R:	Lukas Wunner <lukas@...ner.de>
>  S:	Maintained
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index 8125e5f37832..2456210e85f1 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -65,4 +65,6 @@ source "drivers/vfio/pci/hisilicon/Kconfig"
>  
>  source "drivers/vfio/pci/pds/Kconfig"
>  
> +source "drivers/vfio/pci/nvgrace-gpu/Kconfig"
> +
>  endmenu
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 45167be462d8..1352c65e568a 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -13,3 +13,5 @@ obj-$(CONFIG_MLX5_VFIO_PCI)           += mlx5/
>  obj-$(CONFIG_HISI_ACC_VFIO_PCI) += hisilicon/
>  
>  obj-$(CONFIG_PDS_VFIO_PCI) += pds/
> +
> +obj-$(CONFIG_NVGRACE_GPU_VFIO_PCI) += nvgrace-gpu/
> diff --git a/drivers/vfio/pci/nvgrace-gpu/Kconfig b/drivers/vfio/pci/nvgrace-gpu/Kconfig
> new file mode 100644
> index 000000000000..936e88d8d41d
> --- /dev/null
> +++ b/drivers/vfio/pci/nvgrace-gpu/Kconfig
> @@ -0,0 +1,10 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +config NVGRACE_GPU_VFIO_PCI
> +	tristate "VFIO support for the GPU in the NVIDIA Grace Hopper Superchip"
> +	depends on ARM64 || (COMPILE_TEST && 64BIT)
> +	select VFIO_PCI_CORE
> +	help
> +	  VFIO support for the GPU in the NVIDIA Grace Hopper Superchip is
> +	  required to assign the GPU device using KVM/qemu/etc.
> +
> +	  If you don't know what to do here, say N.
> diff --git a/drivers/vfio/pci/nvgrace-gpu/Makefile b/drivers/vfio/pci/nvgrace-gpu/Makefile
> new file mode 100644
> index 000000000000..3ca8c187897a
> --- /dev/null
> +++ b/drivers/vfio/pci/nvgrace-gpu/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_NVGRACE_GPU_VFIO_PCI) += nvgrace-gpu-vfio-pci.o
> +nvgrace-gpu-vfio-pci-y := main.o
> diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
> new file mode 100644
> index 000000000000..43387a800c41
> --- /dev/null
> +++ b/drivers/vfio/pci/nvgrace-gpu/main.c
> @@ -0,0 +1,806 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved
> + */
> +
> +#include "nvgrace_gpu_vfio_pci.h"

drivers/vfio/pci/nvgrace-gpu/main.c:6:10: fatal error: nvgrace_gpu_vfio_pci.h: No such file or directory
    6 | #include "nvgrace_gpu_vfio_pci.h"


> +
> +static bool nvgrace_gpu_vfio_pci_is_fake_bar(int index)
> +{
> +	return (index == RESMEM_REGION_INDEX ||
> +	    index == USEMEM_REGION_INDEX);
> +}

Presumably these macros are defined in the missing header, though we
don't really need a header file just for that.  This doesn't need to be
line wrapped, it's short enough with the macros as is.
> +
> +static void nvgrace_gpu_init_fake_bar_emu_regs(struct vfio_device *core_vdev)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device,
> +		core_device.vdev);
> +
> +	nvdev->resmem.u64_reg = 0;
> +	nvdev->usemem.u64_reg = 0;
> +}
> +
> +/* Choose the structure corresponding to the fake BAR with a given index. */
> +struct mem_region *
> +nvgrace_gpu_vfio_pci_fake_bar_mem_region(int index,
> +			struct nvgrace_gpu_vfio_pci_core_device *nvdev)
> +{
> +	if (index == USEMEM_REGION_INDEX)
> +		return &(nvdev->usemem);

Parenthesis are unnecessary.

> +
> +	if (index == RESMEM_REGION_INDEX)
> +		return &(nvdev->resmem);
> +
> +	return NULL;
> +}
> +
> +static int nvgrace_gpu_vfio_pci_open_device(struct vfio_device *core_vdev)
> +{
> +	struct vfio_pci_core_device *vdev =
> +		container_of(core_vdev, struct vfio_pci_core_device, vdev);
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device,
> +		core_device.vdev);
> +	int ret;
> +
> +	ret = vfio_pci_core_enable(vdev);
> +	if (ret)
> +		return ret;
> +
> +	vfio_pci_core_finish_enable(vdev);
> +
> +	nvgrace_gpu_init_fake_bar_emu_regs(core_vdev);
> +
> +	mutex_init(&nvdev->remap_lock);
> +
> +	return 0;
> +}
> +
> +static void nvgrace_gpu_vfio_pci_close_device(struct vfio_device *core_vdev)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device,
> +		core_device.vdev);
> +
> +	/* Unmap the mapping to the device memory cached region */
> +	if (nvdev->usemem.bar_remap.memaddr) {
> +		memunmap(nvdev->usemem.bar_remap.memaddr);
> +		nvdev->usemem.bar_remap.memaddr = NULL;
> +	}
> +
> +	/* Unmap the mapping to the device memory non-cached region */
> +	if (nvdev->resmem.bar_remap.ioaddr) {
> +		iounmap(nvdev->resmem.bar_remap.ioaddr);
> +		nvdev->resmem.bar_remap.ioaddr = NULL;
> +	}
> +
> +	mutex_destroy(&nvdev->remap_lock);
> +
> +	vfio_pci_core_close_device(core_vdev);
> +}
> +
> +static int nvgrace_gpu_vfio_pci_mmap(struct vfio_device *core_vdev,
> +				     struct vm_area_struct *vma)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
> +
> +	unsigned long start_pfn;
> +	unsigned int index;
> +	u64 req_len, pgoff, end;
> +	int ret = 0;
> +	struct mem_region *memregion;
> +
> +	index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
> +
> +	memregion = nvgrace_gpu_vfio_pci_fake_bar_mem_region(index, nvdev);
> +	if (!memregion)
> +		return vfio_pci_core_mmap(core_vdev, vma);
> +
> +	/*
> +	 * Request to mmap the BAR. Map to the CPU accessible memory on the
> +	 * GPU using the memory information gathered from the system ACPI
> +	 * tables.
> +	 */
> +	pgoff = vma->vm_pgoff &
> +		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
> +
> +	if (check_sub_overflow(vma->vm_end, vma->vm_start, &req_len) ||
> +		check_add_overflow(PHYS_PFN(memregion->memphys), pgoff, &start_pfn) ||
> +		check_add_overflow(PFN_PHYS(pgoff), req_len, &end))
> +		return -EOVERFLOW;
> +
> +	/*
> +	 * Check that the mapping request does not go beyond available device
> +	 * memory size
> +	 */
> +	if (end > memregion->memlength)
> +		return -EINVAL;
> +
> +	/*
> +	 * The carved out region of the device memory needs the NORMAL_NC
> +	 * property. Communicate as such to the hypervisor.
> +	 */
> +	if (index == RESMEM_REGION_INDEX)
> +		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +
> +	/*
> +	 * Perform a PFN map to the memory and back the device BAR by the
> +	 * GPU memory.
> +	 *
> +	 * The available GPU memory size may not be power-of-2 aligned. Map up
> +	 * to the size of the device memory. If the memory access is beyond the
> +	 * actual GPU memory size, it will be handled by the vfio_device_ops
> +	 * read/write.
> +	 *
> +	 * During device reset, the GPU is safely disconnected to the CPU
> +	 * and access to the BAR will be immediately returned preventing
> +	 * machine check.
> +	 */
> +	ret = remap_pfn_range(vma, vma->vm_start, start_pfn,
> +			      req_len, vma->vm_page_prot);
> +	if (ret)
> +		return ret;
> +
> +	vma->vm_pgoff = start_pfn;
> +
> +	return 0;
> +}
> +
> +static long
> +nvgrace_gpu_vfio_pci_ioctl_get_region_info(struct vfio_device *core_vdev,
> +					    unsigned long arg)
> +{
> +	unsigned long minsz = offsetofend(struct vfio_region_info, offset);
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
> +	struct vfio_region_info_cap_sparse_mmap *sparse;
> +	struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
> +	struct vfio_region_info info;
> +	struct mem_region *memregion;
> +	uint32_t size;
> +	int ret;
> +
> +	if (copy_from_user(&info, (void __user *)arg, minsz))
> +		return -EFAULT;
> +
> +	if (info.argsz < minsz)
> +		return -EINVAL;
> +
> +	memregion = nvgrace_gpu_vfio_pci_fake_bar_mem_region(info.index, nvdev);
> +	if (!memregion)
> +		return vfio_pci_core_ioctl(core_vdev,
> +					   VFIO_DEVICE_GET_REGION_INFO, arg);
> +
> +	/*
> +	 * Request to determine the BAR region information. Send the
> +	 * GPU memory information.
> +	 */
> +	size = struct_size(sparse, areas, 1);
> +
> +	/*
> +	 * Setup for sparse mapping for the device memory. Only the
> +	 * available device memory on the hardware is shown as a
> +	 * mappable region.
> +	 */
> +	sparse = kzalloc(size, GFP_KERNEL);
> +	if (!sparse)
> +		return -ENOMEM;
> +
> +	sparse->nr_areas = 1;
> +	sparse->areas[0].offset = 0;
> +	sparse->areas[0].size = memregion->memlength;
> +	sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> +	sparse->header.version = 1;
> +
> +	ret = vfio_info_add_capability(&caps, &sparse->header, size);
> +	kfree(sparse);
> +	if (ret)
> +		return ret;
> +
> +	info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
> +	/*
> +	 * The region memory size may not be power-of-2 aligned.
> +	 * Given that the memory  as a BAR and may not be
> +	 * aligned, roundup to the next power-of-2.
> +	 */
> +	info.size = roundup_pow_of_two(memregion->memlength);
> +	info.flags = VFIO_REGION_INFO_FLAG_READ |
> +		VFIO_REGION_INFO_FLAG_WRITE |
> +		VFIO_REGION_INFO_FLAG_MMAP;

Align these all:

	info.flags = VFIO_REGION_INFO_FLAG_READ |
		     VFIO_REGION_INFO_FLAG_WRITE |
		     VFIO_REGION_INFO_FLAG_MMAP;

> +
> +	if (caps.size) {
> +		info.flags |= VFIO_REGION_INFO_FLAG_CAPS;
> +		if (info.argsz < sizeof(info) + caps.size) {
> +			info.argsz = sizeof(info) + caps.size;
> +			info.cap_offset = 0;
> +		} else {
> +			vfio_info_cap_shift(&caps, sizeof(info));
> +			if (copy_to_user((void __user *)arg +
> +					 sizeof(info), caps.buf,
> +					 caps.size)) {
> +				kfree(caps.buf);
> +				return -EFAULT;
> +			}
> +			info.cap_offset = sizeof(info);
> +		}
> +		kfree(caps.buf);
> +	}
> +	return copy_to_user((void __user *)arg, &info, minsz) ?
> +			    -EFAULT : 0;
> +}
> +
> +static long nvgrace_gpu_vfio_pci_ioctl(struct vfio_device *core_vdev,
> +					unsigned int cmd, unsigned long arg)
> +{
> +	switch (cmd) {
> +	case VFIO_DEVICE_GET_REGION_INFO:
> +		return nvgrace_gpu_vfio_pci_ioctl_get_region_info(core_vdev, arg);
> +	case VFIO_DEVICE_IOEVENTFD:
> +		return -ENOTTY;
> +	case VFIO_DEVICE_RESET:
> +		nvgrace_gpu_init_fake_bar_emu_regs(core_vdev);
> +		fallthrough;
> +	default:
> +		return vfio_pci_core_ioctl(core_vdev, cmd, arg);
> +	}
> +}
> +
> +static bool range_intersect_range(loff_t range1_start, size_t count1,
> +				  loff_t range2_start, size_t count2,
> +				  loff_t *start_offset,
> +				  size_t *intersect_count,
> +				  size_t *register_offset)
> +{
> +	if (range1_start <= range2_start &&
> +	    range1_start + count1 > range2_start) {
> +		*start_offset = range2_start - range1_start;
> +		*intersect_count = min_t(size_t, count2,
> +					 range1_start + count1 - range2_start);
> +		*register_offset = 0;
> +		return true;
> +	}
> +
> +	if (range1_start > range2_start &&
> +	    range1_start < range2_start + count2) {
> +		*start_offset = 0;
> +		*intersect_count = min_t(size_t, count1,
> +					 range2_start + count2 - range1_start);
> +		*register_offset = range1_start - range2_start;
> +		return true;
> +	}
> +
> +	return false;
> +}

We should put this somewhere shared with virtio-vfio-pci.

> +
> +/*
> + * Both the usable (usemem) and the reserved (resmem) device memory region
> + * are exposed as a 64b fake BARs in the VM. These fake BARs must respond
> + * to the accesses on their respective PCI config space offsets.
> + *
> + * resmem BAR owns PCI_BASE_ADDRESS_2 & PCI_BASE_ADDRESS_3.
> + * usemem BAR owns PCI_BASE_ADDRESS_4 & PCI_BASE_ADDRESS_5.
> + */
> +static ssize_t
> +nvgrace_gpu_read_config_emu(struct vfio_device *core_vdev,
> +			     char __user *buf, size_t count, loff_t *ppos)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
> +	u64 pos = *ppos & VFIO_PCI_OFFSET_MASK;
> +	__le64 val64;
> +	size_t bar_size;
> +	size_t register_offset;
> +	loff_t copy_offset;
> +	size_t copy_count;
> +	int ret;
> +
> +	ret = vfio_pci_core_read(core_vdev, buf, count, ppos);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_2, sizeof(val64),
> +				  &copy_offset, &copy_count, &register_offset)) {
> +		bar_size = roundup_pow_of_two(nvdev->resmem.memlength);
> +		nvdev->resmem.u64_reg &= ~(bar_size - 1);
> +		nvdev->resmem.u64_reg |= PCI_BASE_ADDRESS_MEM_TYPE_64 |
> +					 PCI_BASE_ADDRESS_MEM_PREFETCH;
> +		val64 = cpu_to_le64(nvdev->resmem.u64_reg);

As suggested and implemented in virtio-vfio-pci, store the value as
little endian, then the write function simply becomes a
copy_from_user(), we only need a cpu native representation of the value
on read.

Between this branch and below it looks like you need a helper function
that returns an __le64 provided a __le64 value, u64 mask, and u64 flags.

> +		if (copy_to_user(buf + copy_offset, (void *)&val64 + register_offset, copy_count))
> +			return -EFAULT;
> +	}
> +
> +	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_4, sizeof(val64),
> +				  &copy_offset, &copy_count, &register_offset)) {
> +		bar_size = roundup_pow_of_two(nvdev->usemem.memlength);
> +		nvdev->usemem.u64_reg &= ~(bar_size - 1);
> +		nvdev->usemem.u64_reg |= PCI_BASE_ADDRESS_MEM_TYPE_64 |
> +					 PCI_BASE_ADDRESS_MEM_PREFETCH;
> +		val64 = cpu_to_le64(nvdev->usemem.u64_reg);
> +		if (copy_to_user(buf + copy_offset, (void *)&val64 + register_offset, copy_count))
> +			return -EFAULT;
> +	}
> +
> +	return count;
> +}
> +
> +static ssize_t
> +nvgrace_gpu_write_config_emu(struct vfio_device *core_vdev,
> +			      const char __user *buf, size_t count, loff_t *ppos)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
> +	u64 pos = *ppos & VFIO_PCI_OFFSET_MASK;
> +	__le64 val64 = 0;
> +	__le16 val16 = 0;
> +	u64 tmp_val;
> +	size_t register_offset;
> +	loff_t copy_offset;
> +	size_t copy_count;
> +
> +	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_2, sizeof(val64),
> +				  &copy_offset, &copy_count, &register_offset)) {
> +		if (copy_from_user((void *)&val64, buf + copy_offset, copy_count))
> +			return -EFAULT;
> +		tmp_val = le64_to_cpu(val64);
> +		memcpy((void *)&(nvdev->resmem.u64_reg) + register_offset,
> +			(void *)&tmp_val + copy_offset, copy_count);
> +		*ppos += copy_count;
> +		return copy_count;
> +	}
> +
> +	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_4, sizeof(val64),
> +				  &copy_offset, &copy_count, &register_offset)) {
> +		if (copy_from_user((void *)&val64, buf + copy_offset, copy_count))
> +			return -EFAULT;
> +		tmp_val = le64_to_cpu(val64);
> +		memcpy((void *)&(nvdev->usemem.u64_reg) + register_offset,
> +			(void *)&tmp_val + copy_offset, copy_count);
> +		*ppos += copy_count;
> +		return copy_count;
> +	}
> +
> +	if (range_intersect_range(pos, count, PCI_COMMAND, sizeof(val16),
> +				  &copy_offset, &copy_count, &register_offset)) {
> +		if (copy_from_user((void *)&val16, buf + copy_offset, copy_count))
> +			return -EFAULT;
> +
> +		if (le16_to_cpu(val16) & PCI_COMMAND_MEMORY)
> +			nvdev->bars_disabled = false;
> +		else
> +			nvdev->bars_disabled = true;

nvdev->bars_disabled = !(le16_to_cpu(val16) & PCI_COMMAND_MEMORY);

But you're only tracking COMMAND_MEM relative to user writes, memory
will be disabled on reset and should not initially be enabled.

But then also, isn't this really just an empty token of pretending this
is a PCI BAR if only the read/write and not mmap path honor the device
memory enable bit?  We'd need to zap and restore vmas mapping these
BARs if this was truly behaving as a PCI memory region.

We discussed previously that access through the coherent memory is
unaffected by device reset, is that also true of this non-cached BAR as
well?

TBH, I'm still struggling with the justification to expose these memory
ranges as BAR space versus attaching them as a device specific region
where QEMU would map them into the VM address space and create ACPI
tables to describe them to reflect the same mechanism in the VM as used
on bare metal.  AFAICT the justification boils down to avoiding work in
QEMU and we're sacrificing basic PCI semantics and creating a more
complicated kernel driver to get there.  Let's have an on-list
discussion why this is the correct approach.

> +	}
> +
> +	return vfio_pci_core_write(core_vdev, buf, count, ppos);
> +}
> +
> +/*
> + * Ad hoc map the device memory in the module kernel VA space. Primarily needed
> + * to support Qemu's device x-no-mmap=on option.
> + *
> + * The usemem region is cacheable memory and hence is memremaped.
> + * The resmem region is non-cached and is mapped using ioremap_wc (NORMAL_NC).
> + */
> +static int
> +nvgrace_gpu_map_device_mem(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
> +			    int index)
> +{
> +	int ret = 0;
> +
> +	mutex_lock(&nvdev->remap_lock);
> +	if (index == USEMEM_REGION_INDEX &&
> +		!nvdev->usemem.bar_remap.memaddr) {
> +		nvdev->usemem.bar_remap.memaddr
> +			= memremap(nvdev->usemem.memphys, nvdev->usemem.memlength, MEMREMAP_WB);
> +		if (!nvdev->usemem.bar_remap.memaddr)
> +			ret = -ENOMEM;
> +	} else if (index == RESMEM_REGION_INDEX &&
> +		!nvdev->resmem.bar_remap.ioaddr) {
> +		nvdev->resmem.bar_remap.ioaddr
> +			= ioremap_wc(nvdev->resmem.memphys, nvdev->resmem.memlength);
> +		if (!nvdev->resmem.bar_remap.ioaddr)
> +			ret = -ENOMEM;
> +	}
> +	mutex_unlock(&nvdev->remap_lock);
> +
> +	return ret;
> +}
> +
> +/*
> + * Read the data from the device memory (mapped either through ioremap
> + * or memremap) into the user buffer.
> + */
> +static int
> +nvgrace_gpu_map_and_read(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
> +		void __user *buf, size_t mem_count, loff_t *ppos)
> +{
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	u64 offset = *ppos & VFIO_PCI_OFFSET_MASK;
> +	int ret = 0;
> +
> +	/*
> +	 * Handle read on the BAR regions. Map to the target device memory
> +	 * physical address and copy to the request read buffer.
> +	 */
> +	ret = nvgrace_gpu_map_device_mem(nvdev, index);
> +	if (ret)
> +		goto read_exit;

We don't need a goto to simply return an error.

> +
> +	if (index == USEMEM_REGION_INDEX) {
> +		if (copy_to_user(buf, (u8 *)nvdev->usemem.bar_remap.memaddr + offset, mem_count))
> +			ret = -EFAULT;
> +	} else {
> +		return do_io_rw(&nvdev->core_device, false, nvdev->resmem.bar_remap.ioaddr,
> +				(char __user *) buf, offset, mem_count, 0, 0, false);

The vfio_device_ops.read prototype defines buf as a char __user*, so
maybe look at why it's being passed as a void __user* rather than
casting.

> +	}
> +
> +read_exit:
> +	return ret;
> +}
> +
> +/*
> + * Read count bytes from the device memory at an offset. The actual device
> + * memory size (available) may not be a power-of-2. So the driver fakes
> + * the size to a power-of-2 (reported) when exposing to a user space driver.
> + *
> + * Read request beyond the actual device size is filled with ~0, while
> + * those beyond the actual reported size is skipped.
> + *
> + * A read from a negative or an offset greater than reported size, a negative
> + * count are considered error conditions and returned with an -EINVAL.
> + */
> +static ssize_t
> +nvgrace_gpu_read_mem(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
> +		      void __user *buf, size_t count, loff_t *ppos)
> +{
> +	u64 offset = *ppos & VFIO_PCI_OFFSET_MASK;
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	struct mem_region *memregion;
> +	size_t mem_count, i, bar_size;
> +	u8 val = 0xFF;
> +	int ret;
> +
> +	memregion = nvgrace_gpu_vfio_pci_fake_bar_mem_region(index, nvdev);
> +	if (!memregion)
> +		return -EINVAL;
> +
> +	bar_size = roundup_pow_of_two(memregion->memlength);
> +
> +	if (offset >= bar_size)
> +		return -EINVAL;
> +
> +	/* Clip short the read request beyond reported BAR size */
> +	count = min(count, bar_size - (size_t)offset);
> +
> +	/*
> +	 * Determine how many bytes to be actually read from the device memory.
> +	 * Read request beyond the actual device memory size is filled with ~0,
> +	 * while those beyond the actual reported size is skipped.
> +	 */
> +	if (offset >= memregion->memlength)
> +		mem_count = 0;
> +	else
> +		mem_count = min(count, memregion->memlength - (size_t)offset);
> +
> +	ret = nvgrace_gpu_map_and_read(nvdev, buf, mem_count, ppos);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Only the device memory present on the hardware is mapped, which may
> +	 * not be power-of-2 aligned. A read to an offset beyond the device memory
> +	 * size is filled with ~0.
> +	 */
> +	for (i = mem_count; i < count; i++)
> +		put_user(val, (unsigned char __user *)(buf + i));
> +
> +	*ppos += count;
> +	return count;
> +}
> +
> +static ssize_t
> +nvgrace_gpu_vfio_pci_read(struct vfio_device *core_vdev,
> +			   char __user *buf, size_t count, loff_t *ppos)
> +{
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	ssize_t read_count;
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device,
> +		core_device.vdev);
> +
> +	if (nvgrace_gpu_vfio_pci_is_fake_bar(index)) {

As noted in previous version, we don't need this function:

	if (nvgrace_gpu_vfio_pci_fake_bar_mem_region(index, nvdev)) {

> +		/* Check if the bars are disabled, allow access otherwise */
> +		down_read(&nvdev->core_device.memory_lock);
> +		if (nvdev->bars_disabled) {
> +			up_read(&nvdev->core_device.memory_lock);
> +			return -EIO;
> +		}

Why do we need bars_disabled here, or at all?  If we let do_io_rw()
test memory it would read the command register from vconfig and all of
this is redundant.

> +		read_count = nvgrace_gpu_read_mem(nvdev, buf, count, ppos);
> +		up_read(&nvdev->core_device.memory_lock);
> +
> +		return read_count;
> +	}
> +
> +	if (index == VFIO_PCI_CONFIG_REGION_INDEX)
> +		return nvgrace_gpu_read_config_emu(core_vdev, buf, count, ppos);
> +
> +	return vfio_pci_core_read(core_vdev, buf, count, ppos);
> +}
> +
> +/*
> + * Write the data to the device memory (mapped either through ioremap
> + * or memremap) from the user buffer.
> + */
> +static int nvgrace_gpu_map_and_write(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
> +		const void __user *buf, size_t mem_count, loff_t *ppos)
> +{
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
> +	int ret = 0;
> +
> +	ret = nvgrace_gpu_map_device_mem(nvdev, index);
> +	if (ret)
> +		goto write_exit;
> +
> +	if (index == USEMEM_REGION_INDEX) {
> +		if (copy_from_user((u8 *)nvdev->usemem.bar_remap.memaddr + pos,
> +				   buf, mem_count))
> +			return -EFAULT;
> +	} else {
> +		return do_io_rw(&nvdev->core_device, false, nvdev->resmem.bar_remap.ioaddr,
> +				(char __user *) buf, pos, mem_count, 0, 0, true);
> +	}
> +
> +write_exit:
> +	return ret;
> +}
> +
> +/*
> + * Write count bytes to the device memory at a given offset. The actual device
> + * memory size (available) may not be a power-of-2. So the driver fakes the
> + * size to a power-of-2 (reported) when exposing to a user space driver.
> + *
> + * Write request beyond the actual device size are dropped, while those
> + * beyond the actual reported size are skipped entirely.
> + *
> + * A write to a negative or an offset greater than the reported size, a
> + * negative count are considered error conditions and returned with an -EINVAL.
> + */
> +static ssize_t
> +nvgrace_gpu_write_mem(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
> +			size_t count, loff_t *ppos, const void __user *buf)
> +{
> +	u64 offset = *ppos & VFIO_PCI_OFFSET_MASK;
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	struct mem_region *memregion;
> +	size_t mem_count, bar_size;
> +	int ret = 0;
> +
> +	memregion = nvgrace_gpu_vfio_pci_fake_bar_mem_region(index, nvdev);
> +	if (!memregion)
> +		return -EINVAL;
> +
> +	bar_size = roundup_pow_of_two(memregion->memlength);
> +
> +	if (offset >= bar_size)
> +		return -EINVAL;
> +
> +	/* Clip short the write request beyond reported BAR size */
> +	count = min(count, bar_size - (size_t)offset);
> +
> +	/*
> +	 * Determine how many bytes to be actually written to the device memory.
> +	 * Do not write to the offset beyond available size.
> +	 */
> +	if (offset >= memregion->memlength)
> +		goto exitfn;
> +
> +	/*
> +	 * Only the device memory present on the hardware is mapped, which may
> +	 * not be power-of-2 aligned. Drop access outside the available device
> +	 * memory on the hardware.
> +	 */
> +	mem_count = min(count, memregion->memlength - (size_t)offset);
> +
> +	ret = nvgrace_gpu_map_and_write(nvdev, buf, mem_count, ppos);
> +	if (ret)
> +		return ret;
> +
> +exitfn:
> +	*ppos += count;
> +	return count;
> +}
> +
> +static ssize_t
> +nvgrace_gpu_vfio_pci_write(struct vfio_device *core_vdev,
> +			    const char __user *buf, size_t count, loff_t *ppos)
> +{
> +	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
> +		core_vdev, struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
> +	size_t write_count;
> +
> +	if (nvgrace_gpu_vfio_pci_is_fake_bar(index)) {
> +		/* Check if the bars are disabled, allow access otherwise */
> +		down_read(&nvdev->core_device.memory_lock);
> +		if (nvdev->bars_disabled) {
> +			up_read(&nvdev->core_device.memory_lock);
> +			return -EIO;
> +		}
> +		write_count = nvgrace_gpu_write_mem(nvdev, count, ppos, buf);
> +		up_read(&nvdev->core_device.memory_lock);
> +		return write_count;
> +	}
> +
> +	if (index == VFIO_PCI_CONFIG_REGION_INDEX)
> +		return nvgrace_gpu_write_config_emu(core_vdev, buf, count, ppos);
> +
> +	return vfio_pci_core_write(core_vdev, buf, count, ppos);
> +}
> +
> +static const struct vfio_device_ops nvgrace_gpu_vfio_pci_ops = {
> +	.name = "nvgrace-gpu-vfio-pci",
> +	.init = vfio_pci_core_init_dev,
> +	.release = vfio_pci_core_release_dev,
> +	.open_device = nvgrace_gpu_vfio_pci_open_device,
> +	.close_device = nvgrace_gpu_vfio_pci_close_device,
> +	.ioctl = nvgrace_gpu_vfio_pci_ioctl,
> +	.read = nvgrace_gpu_vfio_pci_read,
> +	.write = nvgrace_gpu_vfio_pci_write,
> +	.mmap = nvgrace_gpu_vfio_pci_mmap,
> +	.request = vfio_pci_core_request,
> +	.match = vfio_pci_core_match,
> +	.bind_iommufd = vfio_iommufd_physical_bind,
> +	.unbind_iommufd = vfio_iommufd_physical_unbind,
> +	.attach_ioas = vfio_iommufd_physical_attach_ioas,
> +	.detach_ioas = vfio_iommufd_physical_detach_ioas,
> +};
> +
> +static struct
> +nvgrace_gpu_vfio_pci_core_device *nvgrace_gpu_drvdata(struct pci_dev *pdev)
> +{
> +	struct vfio_pci_core_device *core_device = dev_get_drvdata(&pdev->dev);
> +
> +	return container_of(core_device, struct nvgrace_gpu_vfio_pci_core_device,
> +			    core_device);
> +}
> +
> +static int
> +nvgrace_gpu_vfio_pci_fetch_memory_property(struct pci_dev *pdev,
> +					    struct nvgrace_gpu_vfio_pci_core_device *nvdev)
> +{
> +	int ret;
> +	u64 memphys, memlength;
> +
> +	/*
> +	 * The memory information is present in the system ACPI tables as DSD
> +	 * properties nvidia,gpu-mem-base-pa and nvidia,gpu-mem-size.
> +	 */
> +	ret = device_property_read_u64(&pdev->dev, "nvidia,gpu-mem-base-pa",
> +				       &(memphys));
> +	if (ret)
> +		return ret;
> +
> +	if (memphys > type_max(phys_addr_t))
> +		return -EOVERFLOW;
> +
> +	ret = device_property_read_u64(&pdev->dev, "nvidia,gpu-mem-size",
> +				       &(memlength));
> +	if (ret)
> +		return ret;
> +
> +	if (memlength > type_max(size_t))
> +		return -EOVERFLOW;
> +
> +	/*
> +	 * If the C2C link is not up due to an error, the coherent device
> +	 * memory size is returned as 0. Fail in such case.
> +	 */
> +	if (memlength == 0)
> +		return -ENOMEM;
> +
> +	/*
> +	 * The VM GPU device driver needs a non-cacheable region to support
> +	 * the MIG feature. Since the device memory is mapped as NORMAL cached,
> +	 * carve out a region from the end with a different NORMAL_NC
> +	 * property (called as reserved memory and represented as resmem). This
> +	 * region then is exposed as a 64b BAR (region 2 and 3) to the VM, while
> +	 * exposing the rest (termed as usable memory and represented using usemem)
> +	 * as cacheable 64b BAR (region 4 and 5).
> +	 *
> +	 *               devmem (memlength)
> +	 * |-------------------------------------------------|
> +	 * |                                           |
> +	 * usemem.phys/memphys                         resmem.phys
> +	 */
> +	nvdev->usemem.memphys = memphys;
> +
> +	/*
> +	 * The device memory exposed to the VM is added to the kernel by the
> +	 * VM driver module in chunks of memory block size. Only the usable
> +	 * memory (usemem) is added to the kernel for usage by the VM
> +	 * workloads. Make the usable memory size memblock aligned.
> +	 */
> +	if (check_sub_overflow(memlength, RESMEM_SIZE,
> +			       &nvdev->usemem.memlength)) {
> +		ret = -EOVERFLOW;
> +		goto done;
> +	}
> +	nvdev->usemem.memlength = round_down(nvdev->usemem.memlength,
> +					     MEMBLK_SIZE);
> +	if ((check_add_overflow(nvdev->usemem.memphys,
> +	     nvdev->usemem.memlength, &nvdev->resmem.memphys)) ||
> +	    (check_sub_overflow(memlength, nvdev->usemem.memlength,
> +	     &nvdev->resmem.memlength))) {
> +		ret = -EOVERFLOW;
> +		goto done;
> +	}
> +
> +done:
> +	return ret;
> +}
> +
> +static int nvgrace_gpu_vfio_pci_probe(struct pci_dev *pdev,
> +				       const struct pci_device_id *id)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev;
> +	int ret;
> +
> +	nvdev = vfio_alloc_device(nvgrace_gpu_vfio_pci_core_device, core_device.vdev,
> +				  &pdev->dev, &nvgrace_gpu_vfio_pci_ops);
> +	if (IS_ERR(nvdev))
> +		return PTR_ERR(nvdev);
> +
> +	dev_set_drvdata(&pdev->dev, nvdev);
> +
> +	ret = nvgrace_gpu_vfio_pci_fetch_memory_property(pdev, nvdev);
> +	if (ret)
> +		goto out_put_vdev;
> +
> +	ret = vfio_pci_core_register_device(&nvdev->core_device);
> +	if (ret)
> +		goto out_put_vdev;
> +
> +	return ret;
> +
> +out_put_vdev:
> +	vfio_put_device(&nvdev->core_device.vdev);
> +	return ret;
> +}
> +
> +static void nvgrace_gpu_vfio_pci_remove(struct pci_dev *pdev)
> +{
> +	struct nvgrace_gpu_vfio_pci_core_device *nvdev = nvgrace_gpu_drvdata(pdev);
> +	struct vfio_pci_core_device *vdev = &nvdev->core_device;
> +
> +	vfio_pci_core_unregister_device(vdev);
> +	vfio_put_device(&vdev->vdev);
> +}
> +
> +static const struct pci_device_id nvgrace_gpu_vfio_pci_table[] = {
> +	/* GH200 120GB */
> +	{ PCI_DRIVER_OVERRIDE_DEVICE_VFIO(PCI_VENDOR_ID_NVIDIA, 0x2342) },
> +	/* GH200 480GB */
> +	{ PCI_DRIVER_OVERRIDE_DEVICE_VFIO(PCI_VENDOR_ID_NVIDIA, 0x2345) },
> +	{}
> +};
> +
> +MODULE_DEVICE_TABLE(pci, nvgrace_gpu_vfio_pci_table);
> +
> +static struct pci_driver nvgrace_gpu_vfio_pci_driver = {
> +	.name = KBUILD_MODNAME,
> +	.id_table = nvgrace_gpu_vfio_pci_table,
> +	.probe = nvgrace_gpu_vfio_pci_probe,
> +	.remove = nvgrace_gpu_vfio_pci_remove,
> +	.err_handler = &vfio_pci_core_err_handlers,
> +	.driver_managed_dma = true,
> +};
> +
> +module_pci_driver(nvgrace_gpu_vfio_pci_driver);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Ankit Agrawal <ankita@...dia.com>");
> +MODULE_AUTHOR("Aniket Agashe <aniketa@...dia.com>");
> +MODULE_DESCRIPTION(
> +	"VFIO NVGRACE GPU PF - User Level driver for NVIDIA devices with CPU coherently accessible device memory");
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index e27de61ac9fe..ca20440b442d 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -94,10 +94,10 @@ VFIO_IOREAD(32)
>   * reads with -1.  This is intended for handling MSI-X vector tables and
>   * leftover space for ROM BARs.
>   */
> -static ssize_t do_io_rw(struct vfio_pci_core_device *vdev, bool test_mem,
> -			void __iomem *io, char __user *buf,
> -			loff_t off, size_t count, size_t x_start,
> -			size_t x_end, bool iswrite)
> +ssize_t do_io_rw(struct vfio_pci_core_device *vdev, bool test_mem,
> +		  void __iomem *io, char __user *buf,
> +		  loff_t off, size_t count, size_t x_start,
> +		  size_t x_end, bool iswrite)

This should be exported in a separate patch and renamed to be
consistent with other vfio-pci-core functions.

>  {
>  	ssize_t done = 0;
>  	int ret;
> @@ -199,6 +199,7 @@ static ssize_t do_io_rw(struct vfio_pci_core_device *vdev, bool test_mem,
>  
>  	return done;
>  }
> +EXPORT_SYMBOL(do_io_rw);

NAK, _GPL.  Thanks,

Alex

>  
>  static int vfio_pci_setup_barmap(struct vfio_pci_core_device *vdev, int bar)
>  {

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