RE: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO

Liu, Yi L
2023-05-15T06:15:05Z

> -----Original Message-----
> From: Baolu Lu <baolu.lu@linux.intel.com>
> Sent: Friday, May 12, 2023 1:39 PM
> To: Liu, Yi L <yi.l.liu@intel.com>; joro@8bytes.org; alex.williamson@redhat.com;
> jgg@nvidia.com; Tian, Kevin <kevin.tian@intel.com>; robin.murphy@arm.com
> Cc: baolu.lu@linux.intel.com; cohuck@redhat.com; eric.auger@redhat.com;
> nicolinc@nvidia.com; kvm@vger.kernel.org; mjrosato@linux.ibm.com;
> chao.p.peng@linux.intel.com; yi.y.sun@linux.intel.com; peterx@redhat.com;
> jasowang@redhat.com; shameerali.kolothum.thodi@huawei.com; lulu@redhat.com;
> suravee.suthikulpanit@amd.com; iommu@lists.linux.dev; linux-kernel@vger.kernel.org;
> linux-kselftest@vger.kernel.org; Duan, Zhenzhong <zhenzhong.duan@intel.com>
> Subject: Re: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO
>
> On 5/11/23 10:30 PM, Yi Liu wrote:
> > Under nested IOMMU translation, userspace owns the stage-1 translation
> > table (e.g. the stage-1 page table of Intel VT-d or the context table
> > of ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific,
> > and needs to be compatiable with the underlying IOMMU hardware. Hence,
> > userspace should know the IOMMU hardware capability before creating and
> > configuring the stage-1 translation table to kernel.
> >
> > This adds IOMMU_DEVICE_GET_HW_INFO to query the IOMMU hardware
> information
> > for a given device. The returned data is vendor specific, userspace needs
> > to decode it with the structure mapped by the @out_data_type field.
> >
> > As only physical devices have IOMMU hardware, so this will return error
> > if the given device is not a physical device.
> >
> > Co-developed-by: Nicolin Chen <nicolinc@nvidia.com>
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> > ---
> > drivers/iommu/iommufd/device.c | 72 +++++++++++++++++++++++++
> > drivers/iommu/iommufd/iommufd_private.h | 1 +
> > drivers/iommu/iommufd/main.c | 3 ++
> > include/uapi/linux/iommufd.h | 37 +++++++++++++
> > 4 files changed, 113 insertions(+)
> >
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index 051bd8e99858..bc99d092de8f 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -263,6 +263,78 @@ u32 iommufd_device_to_id(struct iommufd_device *idev)
> > }
> > EXPORT_SYMBOL_NS_GPL(iommufd_device_to_id, IOMMUFD);
> >
> > +static int iommufd_zero_fill_user(u64 ptr, int bytes)
> > +{
> > + int index = 0;
> > +
> > + for (; index < bytes; index++) {
> > + if (put_user(0, (uint8_t __user *)u64_to_user_ptr(ptr + index)))
> > + return -EFAULT;
> > + }
> > + return 0;
> > +}
> > +
> > +int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
> > +{
> > + struct iommu_hw_info *cmd = ucmd->cmd;
> > + unsigned int length = 0, data_len;
> > + struct iommufd_device *idev;
> > + const struct iommu_ops *ops;
> > + void *data = NULL;
> > + int rc = 0;
> > +
> > + if (cmd->flags || cmd->__reserved || !cmd->data_len)
> > + return -EOPNOTSUPP;
> > +
> > + idev = iommufd_get_device(ucmd, cmd->dev_id);
> > + if (IS_ERR(idev))
> > + return PTR_ERR(idev);
> > +
> > + ops = dev_iommu_ops(idev->dev);
> > + if (!ops->hw_info)
> > + goto done;
>
> If the iommu driver doesn't provide a hw_info callback, it still
> returns success?

Yes, as noted in the cover letter. It's for a remark from Jason. In such
case, the out_data_type is NULL, it means no specific data is filled
in the buffer pointed by cmd->data_ptr.

- Let IOMMU_DEVICE_GET_HW_INFO succeed even the underlying iommu driver
does not have driver-specific data to report per below remark.
https://lore.kernel.org/kvm/ZAcwJSK%2F9UVI9LXu@nvidia.com/

Regards,
Yi Liu

> > +
> > + /* driver has hw_info callback should have a unique hw_info_type */
> > + if (ops->hw_info_type == IOMMU_HW_INFO_TYPE_NONE) {
> > + pr_warn_ratelimited("iommu driver set an invalid type\n");
> > + rc = -ENODEV;
> > + goto out_err;
> > + }
> > +
> > + data = ops->hw_info(idev->dev, &data_len);
> > + if (IS_ERR(data)) {
> > + rc = PTR_ERR(data);
> > + goto out_err;
> > + }
> > +
> > + length = min(cmd->data_len, data_len);
> > + if (copy_to_user(u64_to_user_ptr(cmd->data_ptr), data, length)) {
> > + rc = -EFAULT;
> > + goto out_err;
> > + }
> > +
> > + /*
> > + * Zero the trailing bytes if the user buffer is bigger than the
> > + * data size kernel actually has.
> > + */
> > + if (length < cmd->data_len) {
> > + rc = iommufd_zero_fill_user(cmd->data_ptr + length,
> > + cmd->data_len - length);
> > + if (rc)
> > + goto out_err;
> > + }
> > +
> > +done:
> > + cmd->data_len = length;
> > + cmd->out_data_type = ops->hw_info_type;
> > + rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> > +
> > +out_err:
> > + kfree(data);
> > + iommufd_put_object(&idev->obj);
> > + return rc;
> > +}
> > +
> > static int iommufd_group_setup_msi(struct iommufd_group *igroup,
> > struct iommufd_hw_pagetable *hwpt)
> > {
>
> Best regards,
> baolu