Re: [RFC 10/20] iommu/iommufd: Add IOMMU_DEVICE_GET_INFO

[David Gibson]

On Sun, Sep 19, 2021 at 02:38:38PM +0800, Liu Yi L wrote:
> After a device is bound to the iommufd, userspace can use this interface
> to query the underlying iommu capability and format info for this device.
> Based on this information the user then creates I/O address space in a
> compatible format with the to-be-attached devices.
> 
> Device cookie which is registered at binding time is used to mark the
> device which is being queried here.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> ---
>  drivers/iommu/iommufd/iommufd.c | 68 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/iommu.h      | 49 ++++++++++++++++++++++++
>  2 files changed, 117 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/iommufd.c b/drivers/iommu/iommufd/iommufd.c
> index e16ca21e4534..641f199f2d41 100644
> --- a/drivers/iommu/iommufd/iommufd.c
> +++ b/drivers/iommu/iommufd/iommufd.c
> @@ -117,6 +117,71 @@ static int iommufd_fops_release(struct inode *inode, struct file *filep)
>  	return 0;
>  }
>  
> +static struct device *
> +iommu_find_device_from_cookie(struct iommufd_ctx *ictx, u64 dev_cookie)
> +{
> +	struct iommufd_device *idev;
> +	struct device *dev = NULL;
> +	unsigned long index;
> +
> +	mutex_lock(&ictx->lock);
> +	xa_for_each(&ictx->device_xa, index, idev) {
> +		if (idev->dev_cookie == dev_cookie) {
> +			dev = idev->dev;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&ictx->lock);
> +
> +	return dev;
> +}
> +
> +static void iommu_device_build_info(struct device *dev,
> +				    struct iommu_device_info *info)
> +{
> +	bool snoop;
> +	u64 awidth, pgsizes;
> +
> +	if (!iommu_device_get_info(dev, IOMMU_DEV_INFO_FORCE_SNOOP, &snoop))
> +		info->flags |= snoop ? IOMMU_DEVICE_INFO_ENFORCE_SNOOP : 0;
> +
> +	if (!iommu_device_get_info(dev, IOMMU_DEV_INFO_PAGE_SIZE, &pgsizes)) {
> +		info->pgsize_bitmap = pgsizes;
> +		info->flags |= IOMMU_DEVICE_INFO_PGSIZES;
> +	}
> +
> +	if (!iommu_device_get_info(dev, IOMMU_DEV_INFO_ADDR_WIDTH, &awidth)) {
> +		info->addr_width = awidth;
> +		info->flags |= IOMMU_DEVICE_INFO_ADDR_WIDTH;
> +	}
> +}
> +
> +static int iommufd_get_device_info(struct iommufd_ctx *ictx,
> +				   unsigned long arg)
> +{
> +	struct iommu_device_info info;
> +	unsigned long minsz;
> +	struct device *dev;
> +
> +	minsz = offsetofend(struct iommu_device_info, addr_width);
> +
> +	if (copy_from_user(&info, (void __user *)arg, minsz))
> +		return -EFAULT;
> +
> +	if (info.argsz < minsz)
> +		return -EINVAL;
> +
> +	info.flags = 0;
> +
> +	dev = iommu_find_device_from_cookie(ictx, info.dev_cookie);
> +	if (!dev)
> +		return -EINVAL;
> +
> +	iommu_device_build_info(dev, &info);
> +
> +	return copy_to_user((void __user *)arg, &info, minsz) ? -EFAULT : 0;
> +}
> +
>  static long iommufd_fops_unl_ioctl(struct file *filep,
>  				   unsigned int cmd, unsigned long arg)
>  {
> @@ -127,6 +192,9 @@ static long iommufd_fops_unl_ioctl(struct file *filep,
>  		return ret;
>  
>  	switch (cmd) {
> +	case IOMMU_DEVICE_GET_INFO:
> +		ret = iommufd_get_device_info(ictx, arg);
> +		break;
>  	default:
>  		pr_err_ratelimited("unsupported cmd %u\n", cmd);
>  		break;
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 59178fc229ca..76b71f9d6b34 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -7,6 +7,55 @@
>  #define _UAPI_IOMMU_H
>  
>  #include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +/* -------- IOCTLs for IOMMU file descriptor (/dev/iommu) -------- */
> +
> +#define IOMMU_TYPE	(';')
> +#define IOMMU_BASE	100
> +
> +/*
> + * IOMMU_DEVICE_GET_INFO - _IOR(IOMMU_TYPE, IOMMU_BASE + 1,
> + *				struct iommu_device_info)
> + *
> + * Check IOMMU capabilities and format information on a bound device.
> + *
> + * The device is identified by device cookie (registered when binding
> + * this device).
> + *
> + * @argsz:	   user filled size of this data.
> + * @flags:	   tells userspace which capability info is available
> + * @dev_cookie:	   user assinged cookie.
> + * @pgsize_bitmap: Bitmap of supported page sizes. 1-setting of the
> + *		   bit in pgsize_bitmap[63:12] indicates a supported
> + *		   page size. Details as below table:
> + *
> + *		   +===============+============+
> + *		   |  Bit[index]   |  Page Size |
> + *		   +---------------+------------+
> + *		   |  12           |  4 KB      |
> + *		   +---------------+------------+
> + *		   |  13           |  8 KB      |
> + *		   +---------------+------------+
> + *		   |  14           |  16 KB     |
> + *		   +---------------+------------+
> + *		   ...
> + * @addr_width:    the address width of supported I/O address spaces.
> + *
> + * Availability: after device is bound to iommufd
> + */
> +struct iommu_device_info {
> +	__u32	argsz;
> +	__u32	flags;
> +#define IOMMU_DEVICE_INFO_ENFORCE_SNOOP	(1 << 0) /* IOMMU enforced snoop */
> +#define IOMMU_DEVICE_INFO_PGSIZES	(1 << 1) /* supported page sizes */
> +#define IOMMU_DEVICE_INFO_ADDR_WIDTH	(1 << 2) /* addr_wdith field valid */
> +	__u64	dev_cookie;
> +	__u64   pgsize_bitmap;
> +	__u32	addr_width;

I think this is where you should be reporting available IOVA windows,
rather than just an address width.  I know that for ppc a real
situation will be to have two different windows of different sizes:
that is the effective address width depends on which IOVA window
you're mapping into.


> +};
> +
> +#define IOMMU_DEVICE_GET_INFO	_IO(IOMMU_TYPE, IOMMU_BASE + 1)
>  
>  #define IOMMU_FAULT_PERM_READ	(1 << 0) /* read */
>  #define IOMMU_FAULT_PERM_WRITE	(1 << 1) /* write */

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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