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

[Liu, Yi L]

> -----Original Message-----
> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Friday, May 12, 2023 1:39 PM
> To: Liu, Yi L <yi.l.liu@xxxxxxxxx>; joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> jgg@xxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; robin.murphy@xxxxxxx
> Cc: baolu.lu@xxxxxxxxxxxxxxx; cohuck@xxxxxxxxxx; eric.auger@xxxxxxxxxx;
> nicolinc@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; mjrosato@xxxxxxxxxxxxx;
> chao.p.peng@xxxxxxxxxxxxxxx; yi.y.sun@xxxxxxxxxxxxxxx; peterx@xxxxxxxxxx;
> jasowang@xxxxxxxxxx; shameerali.kolothum.thodi@xxxxxxxxxx; lulu@xxxxxxxxxx;
> suravee.suthikulpanit@xxxxxxx; iommu@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-kselftest@xxxxxxxxxxxxxxx; Duan, Zhenzhong <zhenzhong.duan@xxxxxxxxx>
> 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@xxxxxxxxxx>
> > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx/

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