linux-kernel - Re: [PATCH v1 8/8] vfio/type1: Add vSVA support for IOMMU-backed mdevs

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Message-ID: <20200402143342.1e10c498@w520.home>
Date:   Thu, 2 Apr 2020 14:33:42 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     eric.auger@...hat.com, kevin.tian@...el.com,
        jacob.jun.pan@...ux.intel.com, joro@...tes.org,
        ashok.raj@...el.com, jun.j.tian@...el.com, yi.y.sun@...el.com,
        jean-philippe@...aro.org, peterx@...hat.com,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, hao.wu@...el.com
Subject: Re: [PATCH v1 8/8] vfio/type1: Add vSVA support for IOMMU-backed
 mdevs

On Sun, 22 Mar 2020 05:32:05 -0700
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> From: Liu Yi L <yi.l.liu@...el.com>
> 
> Recent years, mediated device pass-through framework (e.g. vfio-mdev)
> are used to achieve flexible device sharing across domains (e.g. VMs).
> Also there are hardware assisted mediated pass-through solutions from
> platform vendors. e.g. Intel VT-d scalable mode which supports Intel
> Scalable I/O Virtualization technology. Such mdevs are called IOMMU-
> backed mdevs as there are IOMMU enforced DMA isolation for such mdevs.
> In kernel, IOMMU-backed mdevs are exposed to IOMMU layer by aux-domain
> concept, which means mdevs are protected by an iommu domain which is
> aux-domain of its physical device. Details can be found in the KVM
> presentation from Kevin Tian. IOMMU-backed equals to IOMMU-capable.
> 
> https://events19.linuxfoundation.org/wp-content/uploads/2017/12/\
> Hardware-Assisted-Mediated-Pass-Through-with-VFIO-Kevin-Tian-Intel.pdf
> 
> This patch supports NESTING IOMMU for IOMMU-backed mdevs by figuring
> out the physical device of an IOMMU-backed mdev and then invoking IOMMU
> requests to IOMMU layer with the physical device and the mdev's aux
> domain info.
> 
> With this patch, vSVA (Virtual Shared Virtual Addressing) can be used
> on IOMMU-backed mdevs.
> 
> Cc: Kevin Tian <kevin.tian@...el.com>
> CC: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> CC: Jun Tian <jun.j.tian@...el.com>
> Cc: Alex Williamson <alex.williamson@...hat.com>
> Cc: Eric Auger <eric.auger@...hat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 937ec3f..d473665 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -132,6 +132,7 @@ struct vfio_regions {
>  
>  struct domain_capsule {
>  	struct iommu_domain *domain;
> +	struct vfio_group *group;
>  	void *data;
>  };
>  
> @@ -148,6 +149,7 @@ static int vfio_iommu_for_each_dev(struct vfio_iommu *iommu,
>  	list_for_each_entry(d, &iommu->domain_list, next) {
>  		dc.domain = d->domain;
>  		list_for_each_entry(g, &d->group_list, next) {
> +			dc.group = g;
>  			ret = iommu_group_for_each_dev(g->iommu_group,
>  						       &dc, fn);
>  			if (ret)
> @@ -2347,7 +2349,12 @@ static int vfio_bind_gpasid_fn(struct device *dev, void *data)
>  	struct iommu_gpasid_bind_data *gbind_data =
>  		(struct iommu_gpasid_bind_data *) dc->data;
>  
> -	return iommu_sva_bind_gpasid(dc->domain, dev, gbind_data);
> +	if (dc->group->mdev_group)
> +		return iommu_sva_bind_gpasid(dc->domain,
> +			vfio_mdev_get_iommu_device(dev), gbind_data);

But we can't assume an mdev device is iommu backed, so this can call
with NULL dev, which appears will pretty quickly segfault
intel_svm_bind_gpasid.

> +	else
> +		return iommu_sva_bind_gpasid(dc->domain,
> +						dev, gbind_data);
>  }
>  
>  static int vfio_unbind_gpasid_fn(struct device *dev, void *data)
> @@ -2356,8 +2363,13 @@ static int vfio_unbind_gpasid_fn(struct device *dev, void *data)
>  	struct iommu_gpasid_bind_data *gbind_data =
>  		(struct iommu_gpasid_bind_data *) dc->data;
>  
> -	return iommu_sva_unbind_gpasid(dc->domain, dev,
> +	if (dc->group->mdev_group)
> +		return iommu_sva_unbind_gpasid(dc->domain,
> +					vfio_mdev_get_iommu_device(dev),
>  					gbind_data->hpasid);

Same

> +	else
> +		return iommu_sva_unbind_gpasid(dc->domain, dev,
> +						gbind_data->hpasid);
>  }
>  
>  /**
> @@ -2429,7 +2441,12 @@ static int vfio_cache_inv_fn(struct device *dev, void *data)
>  	struct iommu_cache_invalidate_info *cache_inv_info =
>  		(struct iommu_cache_invalidate_info *) dc->data;
>  
> -	return iommu_cache_invalidate(dc->domain, dev, cache_inv_info);
> +	if (dc->group->mdev_group)
> +		return iommu_cache_invalidate(dc->domain,
> +			vfio_mdev_get_iommu_device(dev), cache_inv_info);

And again

> +	else
> +		return iommu_cache_invalidate(dc->domain,
> +						dev, cache_inv_info);
>  }
>  
>  static long vfio_iommu_type1_ioctl(void *iommu_data,