Re: [Qemu-devel] [PATCH 2/3] VFIO driver for mediated PCI device

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 06/21/2016 12:31 AM, Kirti Wankhede wrote:

> +static int mdev_dev_mmio_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	int ret;
> +	struct vfio_mdev *vmdev = vma->vm_private_data;
> +	struct mdev_device *mdev;
> +	struct parent_device *parent;
> +	u64 virtaddr = (u64)vmf->virtual_address;
> +	u64 offset, phyaddr;
> +	unsigned long req_size, pgoff;
> +	pgprot_t pg_prot;
> +
> +	if (!vmdev && !vmdev->mdev)
> +		return -EINVAL;
> +
> +	mdev = vmdev->mdev;
> +	parent  = mdev->parent;
> +
> +	offset   = virtaddr - vma->vm_start;
> +	phyaddr  = (vma->vm_pgoff << PAGE_SHIFT) + offset;
> +	pgoff    = phyaddr >> PAGE_SHIFT;
> +	req_size = vma->vm_end - virtaddr;
> +	pg_prot  = vma->vm_page_prot;
> +
> +	if (parent && parent->ops->validate_map_request) {
> +		mutex_lock(&mdev->ops_lock);
> +		ret = parent->ops->validate_map_request(mdev, virtaddr,
> +							 &pgoff, &req_size,
> +							 &pg_prot);

It is not only 'validate' but also adjust the parameters.

> +		mutex_unlock(&mdev->ops_lock);
> +		if (ret)
> +			return ret;
> +
> +		if (!req_size)
> +			return -EINVAL;
> +	}
> +
> +	ret = remap_pfn_range(vma, virtaddr, pgoff, req_size, pg_prot);
> +

Do you know why
"Issues with mmap region fault handler, EPT is not correctly populated with the
   information provided by remap_pfn_range() inside fault handler."
as you mentioned in the patch 0.

> +	return ret | VM_FAULT_NOPAGE;
> +}
> +
> +static const struct vm_operations_struct mdev_dev_mmio_ops = {
> +	.fault = mdev_dev_mmio_fault,
> +};
> +
> +
> +static int vfio_mpci_mmap(void *device_data, struct vm_area_struct *vma)
> +{
> +	unsigned int index;
> +	struct vfio_mdev *vmdev = device_data;
> +	struct mdev_device *mdev = vmdev->mdev;
> +	struct pci_dev *pdev;
> +	unsigned long pgoff;
> +	loff_t offset;
> +
> +	if (!mdev->parent || !dev_is_pci(mdev->parent->dev))
> +		return -EINVAL;
> +
> +	pdev = to_pci_dev(mdev->parent->dev);
> +
> +	offset = vma->vm_pgoff << PAGE_SHIFT;
> +
> +	index = VFIO_PCI_OFFSET_TO_INDEX(offset);
> +
> +	if (index >= VFIO_PCI_ROM_REGION_INDEX)
> +		return -EINVAL;
> +
> +	pgoff = vma->vm_pgoff &
> +		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
> +
> +	vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff;
> +
> +	vma->vm_private_data = vmdev;
> +	vma->vm_ops = &mdev_dev_mmio_ops;
> +
> +	return 0;
> +}
> +
> +static const struct vfio_device_ops vfio_mpci_dev_ops = {
> +	.name		= "vfio-mpci",
> +	.open		= vfio_mpci_open,
> +	.release	= vfio_mpci_close,
> +	.ioctl		= vfio_mpci_unlocked_ioctl,
> +	.read		= vfio_mpci_read,
> +	.write		= vfio_mpci_write,
> +	.mmap		= vfio_mpci_mmap,
> +};
> +
> +int vfio_mpci_probe(struct device *dev)
> +{
> +	struct vfio_mdev *vmdev;
> +	struct mdev_device *mdev = to_mdev_device(dev);
> +	int ret;
> +
> +	if (!mdev)
> +		return -EINVAL;
> +
> +	vmdev = kzalloc(sizeof(*vmdev), GFP_KERNEL);
> +	if (IS_ERR(vmdev))
> +		return PTR_ERR(vmdev);
> +
> +	vmdev->mdev = mdev_get_device(mdev);
> +	vmdev->group = mdev->group;
> +	mutex_init(&vmdev->vfio_mdev_lock);
> +
> +	ret = vfio_add_group_dev(dev, &vfio_mpci_dev_ops, vmdev);
> +	if (ret)
> +		kfree(vmdev);
> +
> +	mdev_put_device(mdev);

If you can make sure that mdev is always valid during vmdev's lifecyle,
it is not necessary to get and put the refcount of mdev.