linux-kernel - Re: [PATCH v5 1/7] vfio/nvgrace-gpu: Use faults to map device memory

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Message-ID: <20251124171619.GT233636@ziepe.ca>
Date: Mon, 24 Nov 2025 13:16:19 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: ankita@...dia.com
Cc: yishaih@...dia.com, skolothumtho@...dia.com, kevin.tian@...el.com,
	alex@...zbot.org, aniketa@...dia.com, vsethi@...dia.com,
	mochs@...dia.com, Yunxiang.Li@....com, yi.l.liu@...el.com,
	zhangdongdong@...incomputing.com, avihaih@...dia.com,
	bhelgaas@...gle.com, peterx@...hat.com, pstanner@...hat.com,
	apopple@...dia.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, cjia@...dia.com, kwankhede@...dia.com,
	targupta@...dia.com, zhiw@...dia.com, danw@...dia.com,
	dnigam@...dia.com, kjaju@...dia.com
Subject: Re: [PATCH v5 1/7] vfio/nvgrace-gpu: Use faults to map device memory

On Mon, Nov 24, 2025 at 11:59:20AM +0000, ankita@...dia.com wrote:
> From: Ankit Agrawal <ankita@...dia.com>
> 
> To make use of the huge pfnmap support and to support zap/remap
> sequence, fault/huge_fault ops based mapping mechanism needs to
> be implemented.
> 
> Currently nvgrace-gpu module relies on remap_pfn_range to do
> the mapping during VM bootup. Replace it to instead rely on fault
> and use vmf_insert_pfn to setup the mapping.
> 
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  drivers/vfio/pci/nvgrace-gpu/main.c | 50 +++++++++++++++++------------
>  1 file changed, 30 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
> index e346392b72f6..f74f3d8e1ebe 100644
> --- a/drivers/vfio/pci/nvgrace-gpu/main.c
> +++ b/drivers/vfio/pci/nvgrace-gpu/main.c
> @@ -130,6 +130,32 @@ static void nvgrace_gpu_close_device(struct vfio_device *core_vdev)
>  	vfio_pci_core_close_device(core_vdev);
>  }
>  
> +static vm_fault_t nvgrace_gpu_vfio_pci_fault(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct nvgrace_gpu_pci_core_device *nvdev = vma->vm_private_data;
> +	int index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);

This should not be a signed value. I think the right type is unsigned long.

> +	vm_fault_t ret = VM_FAULT_SIGBUS;
> +	struct mem_region *memregion;
> +	unsigned long pgoff, pfn;
> +
> +	memregion = nvgrace_gpu_memregion(index, nvdev);
> +	if (!memregion)
> +		return ret;
> +
> +	pgoff = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
> +	pfn = PHYS_PFN(memregion->memphys) + pgoff;
> +
> +	scoped_guard(rwsem_read, &nvdev->core_device.memory_lock)
> +		ret = vmf_insert_pfn(vmf->vma, vmf->address, pfn);

This needs to check for this:

        if (vdev->pm_runtime_engaged || !__vfio_pci_memory_enabled(vdev))
                goto out_unlock;

So I think your series is out of order.

Move patch 2 before this one, add the above lines to
vfio_pci_vmf_insert_pfn() as well as a lockdep to check the
memory_lock

Then just call vfio_pci_vmf_insert_pfn() here and consider squashing
patch 3.

Jason