linux-kernel - Re: [PATCH v6 1/6] vfio: export function to map the VMA

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Message-ID: <20251125220407.5dba3173.zhiw@nvidia.com>
Date: Tue, 25 Nov 2025 22:04:07 +0200
From: Zhi Wang <zhiw@...dia.com>
To: <ankita@...dia.com>
CC: <jgg@...pe.ca>, <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>, <danw@...dia.com>, <dnigam@...dia.com>,
	<kjaju@...dia.com>
Subject: Re: [PATCH v6 1/6] vfio: export function to map the VMA

On Tue, 25 Nov 2025 17:30:08 +0000
<ankita@...dia.com> wrote:

> From: Ankit Agrawal <ankita@...dia.com>
> 
> Take out the implementation to map the VMA to the PTE/PMD/PUD
> as a separate function.
> 
> Export the function to be used by nvgrace-gpu module.
> 

This looks more like a re-factor than a simple symbol export. Let's add:

No functional change is intended. 

> cc: Shameer Kolothum <skolothumtho@...dia.com>
> cc: Alex Williamson <alex@...zbot.org>
> cc: Jason Gunthorpe <jgg@...pe.ca>

Nit: I saw "cc" tag is also used somewhere else in the git log. I was
suprised that checkpatch.pl doesn't complain about it. I did test it.

In VFIO, people tend to use "Cc:" according to a search of the git log.
Let's keep using "Cc:" in VFIO.

> Reviewed-by: Shameer Kolothum <skolothumtho@...dia.com>
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 50
> ++++++++++++++++++++------------ include/linux/vfio_pci_core.h    |
> 3 ++ 2 files changed, 34 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c
> b/drivers/vfio/pci/vfio_pci_core.c index 7dcf5439dedc..c445a53ee12e
> 100644 --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1640,31 +1640,21 @@ static unsigned long vma_to_pfn(struct
> vm_area_struct *vma) return (pci_resource_start(vdev->pdev, index) >>
> PAGE_SHIFT) + pgoff; }
>  
> -static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
> -					   unsigned int order)
> +vm_fault_t vfio_pci_vmf_insert_pfn(struct vfio_pci_core_device *vdev,
> +				   struct vm_fault *vmf,
> +				   unsigned long pfn,
> +				   unsigned int order)
>  {
> -	struct vm_area_struct *vma = vmf->vma;
> -	struct vfio_pci_core_device *vdev = vma->vm_private_data;
> -	unsigned long addr = vmf->address & ~((PAGE_SIZE << order) -
> 1);
> -	unsigned long pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
> -	unsigned long pfn = vma_to_pfn(vma) + pgoff;
> -	vm_fault_t ret = VM_FAULT_SIGBUS;
> +	vm_fault_t ret;
>  
> -	if (order && (addr < vma->vm_start ||
> -		      addr + (PAGE_SIZE << order) > vma->vm_end ||
> -		      pfn & ((1 << order) - 1))) {
> -		ret = VM_FAULT_FALLBACK;
> -		goto out;
> -	}
> -
> -	down_read(&vdev->memory_lock);
> +	lockdep_assert_held_read(&vdev->memory_lock);
>  
>  	if (vdev->pm_runtime_engaged ||
> !__vfio_pci_memory_enabled(vdev))
> -		goto out_unlock;
> +		return VM_FAULT_SIGBUS;
>  
>  	switch (order) {
>  	case 0:
> -		ret = vmf_insert_pfn(vma, vmf->address, pfn);
> +		ret = vmf_insert_pfn(vmf->vma, vmf->address, pfn);
>  		break;
>  #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
>  	case PMD_ORDER:
> @@ -1680,7 +1670,29 @@ static vm_fault_t
> vfio_pci_mmap_huge_fault(struct vm_fault *vmf, ret =
> VM_FAULT_FALLBACK; }
>  
> -out_unlock:
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(vfio_pci_vmf_insert_pfn);
> +
> +static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
> +					   unsigned int order)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct vfio_pci_core_device *vdev = vma->vm_private_data;
> +	unsigned long addr = vmf->address & ~((PAGE_SIZE << order) -
> 1);
> +	unsigned long pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
> +	unsigned long pfn = vma_to_pfn(vma) + pgoff;
> +	vm_fault_t ret = VM_FAULT_SIGBUS;
> +
> +	if (order && (addr < vma->vm_start ||
> +		      addr + (PAGE_SIZE << order) > vma->vm_end ||
> +		      pfn & ((1 << order) - 1))) {
> +		ret = VM_FAULT_FALLBACK;
> +		goto out;
> +	}
> +
> +	down_read(&vdev->memory_lock);
> +	ret = vfio_pci_vmf_insert_pfn(vdev, vmf, pfn, order);
>  	up_read(&vdev->memory_lock);
>  out:
>  	dev_dbg_ratelimited(&vdev->pdev->dev,
> diff --git a/include/linux/vfio_pci_core.h
> b/include/linux/vfio_pci_core.h index f541044e42a2..6f7c6c0d4278
> 100644 --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -119,6 +119,9 @@ ssize_t vfio_pci_core_read(struct vfio_device
> *core_vdev, char __user *buf, size_t count, loff_t *ppos);
>  ssize_t vfio_pci_core_write(struct vfio_device *core_vdev, const
> char __user *buf, size_t count, loff_t *ppos);
> +vm_fault_t vfio_pci_vmf_insert_pfn(struct vfio_pci_core_device *vdev,
> +				   struct vm_fault *vmf, unsigned
> long pfn,
> +				   unsigned int order);
>  int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct
> vm_area_struct *vma); void vfio_pci_core_request(struct vfio_device
> *core_vdev, unsigned int count); int vfio_pci_core_match(struct
> vfio_device *core_vdev, char *buf);