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

[Baolu Lu]

On 5/15/23 2:14 PM, Liu, Yi L wrote:
> > -----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/

Oh, I overlooked that. Thanks for the explanation. It's fair enough.

Best regards,
baolu