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

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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@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: Dongwon Kim <dongwon.kim@xxxxxxxxx>
Cc: Junxiao Chang <junxiao.chang@xxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
  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@xxxxxxxxxx>

--
Cheers,

David / dhildenb





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