Re: [PATCH v2 1/2] udmabuf: Use vmf_insert_pfn and VM_PFNMAP for handling mmap

[David Hildenbrand <david@redhat.com>]

On 18.07.23 10:26, Vivek Kasireddy wrote:
> Add VM_PFNMAP to vm_flags in the mmap handler to ensure that
> the mappings would be managed without using struct page.
> 
> And, in the vm_fault handler, use vmf_insert_pfn to share the
> page's pfn to userspace instead of directly sharing the page
> (via struct page *).
> 
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Jason Gunthorpe <jgg@nvidia.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Dongwon Kim <dongwon.kim@intel.com>
> Cc: Junxiao Chang <junxiao.chang@intel.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>   drivers/dma-buf/udmabuf.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..820c993c8659 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -35,12 +35,13 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
>   	struct vm_area_struct *vma = vmf->vma;
>   	struct udmabuf *ubuf = vma->vm_private_data;
>   	pgoff_t pgoff = vmf->pgoff;
> +	unsigned long pfn;
>   
>   	if (pgoff >= ubuf->pagecount)
>   		return VM_FAULT_SIGBUS;
> -	vmf->page = ubuf->pages[pgoff];
> -	get_page(vmf->page);
> -	return 0;
> +
> +	pfn = page_to_pfn(ubuf->pages[pgoff]);
> +	return vmf_insert_pfn(vma, vmf->address, pfn);
>   }
>   
>   static const struct vm_operations_struct udmabuf_vm_ops = {
> @@ -56,6 +57,7 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
>   
>   	vma->vm_ops = &udmabuf_vm_ops;
>   	vma->vm_private_data = ubuf;
> +	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
>   	return 0;
>   }
>   

Looks reasonable to me.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb