On Tue, 28 Apr 2020 14:49:57 -0300 Jason Gunthorpe jgg@ziepe.ca wrote:
On Tue, Apr 28, 2020 at 10:54:55AM -0600, Alex Williamson wrote:
static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) { struct vfio_pci_device *vdev = device_data; @@ -1253,8 +1323,14 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff;
- vma->vm_ops = &vfio_pci_mmap_ops;
+#if 1
- return 0;
+#else return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
req_len, vma->vm_page_prot);
vma->vm_end - vma->vm_start, vma->vm_page_prot);The remap_pfn_range here is what tells get_user_pages this is a non-struct page mapping:
vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
Which has to be set when the VMA is created, they shouldn't be modified during fault.
Aha, thanks Jason! So fundamentally, pin_user_pages_remote() should never have been faulting in this vma since the pages are non-struct page backed. Maybe I was just getting lucky before this commit. For a VM_PFNMAP, vaddr_get_pfn() only needs pin_user_pages_remote() to return error and the vma information that we setup in vfio_pci_mmap(). We only need the fault handler to trigger for user access, which is what I see with this change. That should work for me.
Also the vma code above looked a little strange to me, if you do send something like this cc me and I can look at it. I did some work like this for rdma a while ago..
Cool, I'll do that. I'd like to be able to zap the vmas from user access at a later point and I have doubts that I'm holding the refs/locks that I need to for that. Thanks,
Alex