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Date:   Wed, 1 Apr 2020 17:49:32 +0200
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Bharat Bhushan <bbhushan2@marvell.com>, joro@8bytes.org,
        mst@redhat.com, jasowang@redhat.com,
        virtualization@lists.linux-foundation.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        eric.auger.pro@gmail.com, eric.auger@redhat.com
Subject: Re: [RFC PATCH v2] iommu/virtio: Use page size bitmap supported by
 endpoint
Message-ID: <20200401154932.GA1124215@myrica>
References: <20200401113804.21616-1-bbhushan2@marvell.com>
 <b75beb74-89ce-fd6a-6207-3c0d7f479215@arm.com>
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On Wed, Apr 01, 2020 at 02:00:13PM +0100, Robin Murphy wrote:
> On 2020-04-01 12:38 pm, Bharat Bhushan wrote:
> > Different endpoint can support different page size, probe
> > endpoint if it supports specific page size otherwise use
> > global page sizes.
> > 
> > Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
> > ---
> >   drivers/iommu/virtio-iommu.c      | 33 +++++++++++++++++++++++++++----
> >   include/uapi/linux/virtio_iommu.h |  7 +++++++
> >   2 files changed, 36 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> > index cce329d71fba..c794cb5b7b3e 100644
> > --- a/drivers/iommu/virtio-iommu.c
> > +++ b/drivers/iommu/virtio-iommu.c
> > @@ -78,6 +78,7 @@ struct viommu_endpoint {
> >   	struct viommu_dev		*viommu;
> >   	struct viommu_domain		*vdomain;
> >   	struct list_head		resv_regions;
> > +	u64				pgsize_bitmap;
> >   };
> >   struct viommu_request {
> > @@ -415,6 +416,20 @@ static int viommu_replay_mappings(struct viommu_domain *vdomain)
> >   	return ret;
> >   }
> > +static int viommu_set_pgsize_bitmap(struct viommu_endpoint *vdev,
> > +				    struct virtio_iommu_probe_pgsize_mask *mask,
> > +				    size_t len)
> > +
> > +{
> > +	u64 pgsize_bitmap = le64_to_cpu(mask->pgsize_bitmap);
> > +
> > +	if (len < sizeof(*mask))
> > +		return -EINVAL;
> > +
> > +	vdev->pgsize_bitmap = pgsize_bitmap;
> > +	return 0;
> > +}
> > +
> >   static int viommu_add_resv_mem(struct viommu_endpoint *vdev,
> >   			       struct virtio_iommu_probe_resv_mem *mem,
> >   			       size_t len)
> > @@ -494,11 +509,13 @@ static int viommu_probe_endpoint(struct viommu_dev *viommu, struct device *dev)
> >   	while (type != VIRTIO_IOMMU_PROBE_T_NONE &&
> >   	       cur < viommu->probe_size) {
> >   		len = le16_to_cpu(prop->length) + sizeof(*prop);
> > -

Whitespace change

> >   		switch (type) {
> >   		case VIRTIO_IOMMU_PROBE_T_RESV_MEM:
> >   			ret = viommu_add_resv_mem(vdev, (void *)prop, len);
> >   			break;
> > +		case VIRTIO_IOMMU_PROBE_T_PAGE_SIZE_MASK:
> > +			ret = viommu_set_pgsize_bitmap(vdev, (void *)prop, len);
> > +			break;
> >   		default:
> >   			dev_err(dev, "unknown viommu prop 0x%x\n", type);
> >   		}
> > @@ -607,16 +624,23 @@ static struct iommu_domain *viommu_domain_alloc(unsigned type)
> >   	return &vdomain->domain;
> >   }
> > -static int viommu_domain_finalise(struct viommu_dev *viommu,
> > +static int viommu_domain_finalise(struct viommu_endpoint *vdev,
> >   				  struct iommu_domain *domain)
> >   {
> >   	int ret;
> >   	struct viommu_domain *vdomain = to_viommu_domain(domain);
> > +	struct viommu_dev *viommu = vdev->viommu;
> >   	vdomain->viommu		= viommu;
> >   	vdomain->map_flags	= viommu->map_flags;
> > -	domain->pgsize_bitmap	= viommu->pgsize_bitmap;
> > +	/* Devices in same domain must support same size pages */
> 
> AFAICS what the code appears to do is enforce that the first endpoint
> attached to any domain has the same pgsize_bitmap as the most recently
> probed viommu_dev instance, then ignore any subsequent endpoints attached to
> the same domain. Thus I'm not sure that comment is accurate.
> 

Yes viommu_domain_finalise() is only called once. What I had in mind is
something like:

---- 8< ----
diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 750f69c49b95..8303b7b513ff 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -639,6 +639,29 @@ static int viommu_domain_finalise(struct viommu_endpoint *vdev,
 	return 0;
 }
 
+/*
+ * Check whether the endpoint's capabilities are compatible with other endpoints
+ * in the domain. Report any inconsistency.
+ */
+static bool viommu_endpoint_is_compatible(struct viommu_endpoint *vdev,
+					  struct viommu_domain *vdomain)
+{
+	struct device *dev = vdev->dev;
+
+	if (vdomain->viommu != vdev->viommu) {
+		dev_err(dev, "cannot attach to foreign vIOMMU\n");
+		return false;
+	}
+
+	if (vdomain->domain.pgsize_bitmap != vdev->pgsize_bitmap) {
+		dev_err(dev, "incompatible domain bitmap 0x%lx != 0x%lx\n",
+			vdomain->domain.pgsize_bitmap, vdev->pgsize_bitmap);
+		return false;
+	}
+
+	return true;
+}
+
 static void viommu_domain_free(struct iommu_domain *domain)
 {
 	struct viommu_domain *vdomain = to_viommu_domain(domain);
@@ -670,9 +693,8 @@ static int viommu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		 * owns it.
 		 */
 		ret = viommu_domain_finalise(vdev, domain);
-	} else if (vdomain->viommu != vdev->viommu) {
-		dev_err(dev, "cannot attach to foreign vIOMMU\n");
-		ret = -EXDEV;
+	} else if (!viommu_endpoint_is_compatible(vdev, vdomain)) {
+		ret = -EINVAL;
 	}
 	mutex_unlock(&vdomain->mutex);
---- >8 ----

> 
> > +	if ((domain->pgsize_bitmap != viommu->pgsize_bitmap) &&
> > +	    (domain->pgsize_bitmap != vdev->pgsize_bitmap))
> > +		return -EINVAL;
> > +
> > +	domain->pgsize_bitmap = vdev->pgsize_bitmap;
> > +
> >   	domain->geometry	= viommu->geometry;
> >   	ret = ida_alloc_range(&viommu->domain_ids, viommu->first_domain,
> > @@ -657,7 +681,7 @@ static int viommu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >   		 * Properly initialize the domain now that we know which viommu
> >   		 * owns it.
> >   		 */
> > -		ret = viommu_domain_finalise(vdev->viommu, domain);
> > +		ret = viommu_domain_finalise(vdev, domain);
> >   	} else if (vdomain->viommu != vdev->viommu) {
> >   		dev_err(dev, "cannot attach to foreign vIOMMU\n");
> >   		ret = -EXDEV;
> > @@ -875,6 +899,7 @@ static int viommu_add_device(struct device *dev)
> >   	vdev->dev = dev;
> >   	vdev->viommu = viommu;
> > +	vdev->pgsize_bitmap = viommu->pgsize_bitmap;
> >   	INIT_LIST_HEAD(&vdev->resv_regions);
> >   	fwspec->iommu_priv = vdev;
> > diff --git a/include/uapi/linux/virtio_iommu.h b/include/uapi/linux/virtio_iommu.h
> > index 237e36a280cb..dc9d3f40bcd8 100644
> > --- a/include/uapi/linux/virtio_iommu.h
> > +++ b/include/uapi/linux/virtio_iommu.h
> > @@ -111,6 +111,7 @@ struct virtio_iommu_req_unmap {
> >   #define VIRTIO_IOMMU_PROBE_T_NONE		0
> >   #define VIRTIO_IOMMU_PROBE_T_RESV_MEM		1
> > +#define VIRTIO_IOMMU_PROBE_T_PAGE_SIZE_MASK	2
> >   #define VIRTIO_IOMMU_PROBE_T_MASK		0xfff
> > @@ -119,6 +120,12 @@ struct virtio_iommu_probe_property {
> >   	__le16					length;
> >   };
> > +struct virtio_iommu_probe_pgsize_mask {
> > +	struct virtio_iommu_probe_property	head;
> > +	__u8					reserved[4];
> > +	__u64					pgsize_bitmap;

Should be __le64

Thanks,
Jean

> > +};
> > +
> >   #define VIRTIO_IOMMU_RESV_MEM_T_RESERVED	0
> >   #define VIRTIO_IOMMU_RESV_MEM_T_MSI		1
> >