Re: [PATCH v2 11/11] iommufd: Allow iommufd to supply /dev/vfio/vfio

[Yi Liu <yi.l.liu@intel.com>]

On 2022/11/8 08:52, Jason Gunthorpe wrote:
> If the VFIO container is compiled out, give a kconfig option for iommufd
> to provide the miscdev node with the same name and permissions as vfio
> uses.
> 
> The compatibility node supports the same ioctls as VFIO and automatically
> enables the VFIO compatible pinned page accounting mode.
> 
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>   drivers/iommu/iommufd/Kconfig | 12 ++++++++++++
>   drivers/iommu/iommufd/main.c  | 36 +++++++++++++++++++++++++++++++++++
>   2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/Kconfig b/drivers/iommu/iommufd/Kconfig
> index 399a2edeaef6de..f387f803dc6f7f 100644
> --- a/drivers/iommu/iommufd/Kconfig
> +++ b/drivers/iommu/iommufd/Kconfig
> @@ -12,6 +12,18 @@ config IOMMUFD
>   	  If you don't know what to do here, say N.
>   
>   if IOMMUFD
> +config IOMMUFD_VFIO_CONTAINER
> +	bool "IOMMUFD provides the VFIO container /dev/vfio/vfio"
> +	depends on VFIO && !VFIO_CONTAINER
> +	default VFIO && !VFIO_CONTAINER
> +	help
> +	  IOMMUFD will provide /dev/vfio/vfio instead of VFIO. This relies on
> +	  IOMMUFD providing compatibility emulation to give the same ioctls.
> +	  It provides an option to build a kernel with legacy VFIO components
> +	  removed.
> +
> +	  Unless testing IOMMUFD say N here.
> +
>   config IOMMUFD_TEST
>   	bool "IOMMU Userspace API Test support"
>   	depends on RUNTIME_TESTING_MENU
> diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
> index ab3fa05f38505d..1eeb326f74f005 100644
> --- a/drivers/iommu/iommufd/main.c
> +++ b/drivers/iommu/iommufd/main.c
> @@ -18,6 +18,7 @@
>   #include <uapi/linux/iommufd.h>
>   #include <linux/iommufd.h>
>   
> +#include "io_pagetable.h"
>   #include "iommufd_private.h"
>   #include "iommufd_test.h"
>   
> @@ -25,6 +26,7 @@ struct iommufd_object_ops {
>   	void (*destroy)(struct iommufd_object *obj);
>   };
>   static const struct iommufd_object_ops iommufd_object_ops[];
> +static struct miscdevice vfio_misc_dev;
>   
>   struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
>   					     size_t size,
> @@ -170,6 +172,16 @@ static int iommufd_fops_open(struct inode *inode, struct file *filp)
>   	if (!ictx)
>   		return -ENOMEM;
>   
> +	/*
> +	 * For compatibility with VFIO when /dev/vfio/vfio is opened we default
> +	 * to the same rlimit accounting as vfio uses.
> +	 */
> +	if (IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER) &&
> +	    filp->private_data == &vfio_misc_dev) {
> +		ictx->account_mode = IOPT_PAGES_ACCOUNT_MM;
> +		pr_info_once("IOMMUFD is providing /dev/vfio/vfio, not VFIO.\n");
> +	}
> +
>   	xa_init_flags(&ictx->objects, XA_FLAGS_ALLOC1 | XA_FLAGS_ACCOUNT);
>   	ictx->file = filp;
>   	filp->private_data = ictx;
> @@ -395,6 +407,15 @@ static struct miscdevice iommu_misc_dev = {
>   	.mode = 0660,
>   };
>   
> +
> +static struct miscdevice vfio_misc_dev = {
> +	.minor = VFIO_MINOR,
> +	.name = "vfio",
> +	.fops = &iommufd_fops,
> +	.nodename = "vfio/vfio",
> +	.mode = 0666,
> +};
> +
>   static int __init iommufd_init(void)
>   {
>   	int ret;
> @@ -402,18 +423,33 @@ static int __init iommufd_init(void)
>   	ret = misc_register(&iommu_misc_dev);
>   	if (ret)
>   		return ret;
> +
> +	if (IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER)) {
> +		ret = misc_register(&vfio_misc_dev);
> +		if (ret)
> +			goto err_misc;
> +	}
>   	iommufd_test_init();
>   	return 0;
> +err_misc:
> +	misc_deregister(&iommu_misc_dev);
> +	return ret;
>   }
>   
>   static void __exit iommufd_exit(void)
>   {
>   	iommufd_test_exit();
> +	if (IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER))
> +		misc_deregister(&vfio_misc_dev);
>   	misc_deregister(&iommu_misc_dev);
>   }
>   
>   module_init(iommufd_init);
>   module_exit(iommufd_exit);
>   
> +#if IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER)
> +MODULE_ALIAS_MISCDEV(VFIO_MINOR);
> +MODULE_ALIAS("devname:vfio/vfio");

will this line also result in systemd to create this devnodes at boot
based on the module info even if the IOMMUFD_VFIO_CONTAINER is not
configured?

> +#endif
>   MODULE_DESCRIPTION("I/O Address Space Management for passthrough devices");
>   MODULE_LICENSE("GPL");

-- 
Regards,
Yi Liu