thr3ads.net - Linux Virtualization - [PATCH 2/5] iommu/virtio: Support bypass domains [Oct 2021]

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Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

[PATCH 0/5] iommu/virtio: Add identity domains

Support identity domains, allowing to only enable IOMMU protection for a
subset of endpoints (those assigned to userspace, for example). Users
may enable identity domains at compile time
(CONFIG_IOMMU_DEFAULT_PASSTHROUGH), boot time (iommu.passthrough=1) or
runtime (/sys/kernel/iommu_groups/*/type = identity).

Patches 1-2 support identity domains using the optional
VIRTIO_IOMMU_F_BYPASS_CONFIG feature. The feature bit is not yet in the
spec, see [1] for the latest proposal.

Patches 3-5 add a fallback to identity mappings, when the feature is not
supported.

Note that this series doesn't touch the global bypass bit added by
VIRTIO_IOMMU_F_BYPASS_CONFIG. All endpoints managed by the IOMMU should
be attached to a domain, so global bypass isn't in use after endpoints
are probed. Before that, the global bypass policy is decided by the
hypervisor and firmware. So I don't think Linux needs to touch the
global bypass bit, but there are some patches available on my
virtio-iommu/bypass branch [2] to test it.

QEMU patches are on my virtio-iommu/bypass branch [3] (and the list)

[1] https://www.mail-archive.com/virtio-dev at
lists.oasis-open.org/msg07898.html
[2] https://jpbrucker.net/git/linux/log/?h=virtio-iommu/bypass
[3] https://jpbrucker.net/git/qemu/log/?h=virtio-iommu/bypass

Jean-Philippe Brucker (5):
  iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG
  iommu/virtio: Support bypass domains
  iommu/virtio: Sort reserved regions
  iommu/virtio: Pass end address to viommu_add_mapping()
  iommu/virtio: Support identity-mapped domains

 include/uapi/linux/virtio_iommu.h |   8 ++-
 drivers/iommu/virtio-iommu.c      | 113 +++++++++++++++++++++++++-----
 2 files changed, 101 insertions(+), 20 deletions(-)

-- 
2.33.0

Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

head link

[PATCH 1/5] iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG

Add definitions for the VIRTIO_IOMMU_F_BYPASS_CONFIG, which supersedes
VIRTIO_IOMMU_F_BYPASS.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 include/uapi/linux/virtio_iommu.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/virtio_iommu.h
b/include/uapi/linux/virtio_iommu.h
index 237e36a280cb..cafd8cf7febf 100644
--- a/include/uapi/linux/virtio_iommu.h
+++ b/include/uapi/linux/virtio_iommu.h
@@ -16,6 +16,7 @@
 #define VIRTIO_IOMMU_F_BYPASS			3
 #define VIRTIO_IOMMU_F_PROBE			4
 #define VIRTIO_IOMMU_F_MMIO			5
+#define VIRTIO_IOMMU_F_BYPASS_CONFIG		6
 
 struct virtio_iommu_range_64 {
 	__le64					start;
@@ -36,6 +37,8 @@ struct virtio_iommu_config {
 	struct virtio_iommu_range_32		domain_range;
 	/* Probe buffer size */
 	__le32					probe_size;
+	__u8					bypass;
+	__u8					reserved[7];
 };
 
 /* Request types */
@@ -66,11 +69,14 @@ struct virtio_iommu_req_tail {
 	__u8					reserved[3];
 };
 
+#define VIRTIO_IOMMU_ATTACH_F_BYPASS		(1 << 0)
+
 struct virtio_iommu_req_attach {
 	struct virtio_iommu_req_head		head;
 	__le32					domain;
 	__le32					endpoint;
-	__u8					reserved[8];
+	__le32					flags;
+	__u8					reserved[4];
 	struct virtio_iommu_req_tail		tail;
 };
 
-- 
2.33.0

Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

head link

[PATCH 2/5] iommu/virtio: Support bypass domains

The VIRTIO_IOMMU_F_BYPASS_CONFIG feature adds a new flag to the ATTACH
request, that creates a bypass domain. Use it to enable identity
domains.

When VIRTIO_IOMMU_F_BYPASS_CONFIG is not supported by the device, we
currently fail attaching to an identity domain. Future patches will
instead create identity mappings in this case.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 drivers/iommu/virtio-iommu.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 80930ce04a16..ee8a7afd667b 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -71,6 +71,7 @@ struct viommu_domain {
 	struct rb_root_cached		mappings;
 
 	unsigned long			nr_endpoints;
+	bool				bypass;
 };
 
 struct viommu_endpoint {
@@ -587,7 +588,9 @@ static struct iommu_domain *viommu_domain_alloc(unsigned
type)
 {
 	struct viommu_domain *vdomain;
 
-	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
+	if (type != IOMMU_DOMAIN_UNMANAGED &&
+	    type != IOMMU_DOMAIN_DMA &&
+	    type != IOMMU_DOMAIN_IDENTITY)
 		return NULL;
 
 	vdomain = kzalloc(sizeof(*vdomain), GFP_KERNEL);
@@ -630,6 +633,17 @@ static int viommu_domain_finalise(struct viommu_endpoint
*vdev,
 	vdomain->map_flags	= viommu->map_flags;
 	vdomain->viommu		= viommu;
 
+	if (domain->type == IOMMU_DOMAIN_IDENTITY) {
+		if (!virtio_has_feature(viommu->vdev,
+					VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
+			ida_free(&viommu->domain_ids, vdomain->id);
+			vdomain->viommu = 0;
+			return -EOPNOTSUPP;
+		}
+
+		vdomain->bypass = true;
+	}
+
 	return 0;
 }
 
@@ -691,6 +705,9 @@ static int viommu_attach_dev(struct iommu_domain *domain,
struct device *dev)
 		.domain		= cpu_to_le32(vdomain->id),
 	};
 
+	if (vdomain->bypass)
+		req.flags |= cpu_to_le32(VIRTIO_IOMMU_ATTACH_F_BYPASS);
+
 	for (i = 0; i < fwspec->num_ids; i++) {
 		req.endpoint = cpu_to_le32(fwspec->ids[i]);
 
@@ -1132,6 +1149,7 @@ static unsigned int features[] = {
 	VIRTIO_IOMMU_F_DOMAIN_RANGE,
 	VIRTIO_IOMMU_F_PROBE,
 	VIRTIO_IOMMU_F_MMIO,
+	VIRTIO_IOMMU_F_BYPASS_CONFIG,
 };
 
 static struct virtio_device_id id_table[] = {
-- 
2.33.0

Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

head link

[PATCH 3/5] iommu/virtio: Sort reserved regions

To ease identity mapping support, keep the list of reserved regions
sorted.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 drivers/iommu/virtio-iommu.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index ee8a7afd667b..d63ec4d11b00 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -423,7 +423,7 @@ static int viommu_add_resv_mem(struct viommu_endpoint *vdev,
 	size_t size;
 	u64 start64, end64;
 	phys_addr_t start, end;
-	struct iommu_resv_region *region = NULL;
+	struct iommu_resv_region *region = NULL, *next;
 	unsigned long prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
 
 	start = start64 = le64_to_cpu(mem->start);
@@ -454,7 +454,12 @@ static int viommu_add_resv_mem(struct viommu_endpoint
*vdev,
 	if (!region)
 		return -ENOMEM;
 
-	list_add(&region->list, &vdev->resv_regions);
+	/* Keep the list sorted */
+	list_for_each_entry(next, &vdev->resv_regions, list) {
+		if (next->start > region->start)
+			break;
+	}
+	list_add_tail(&region->list, &next->list);
 	return 0;
 }
 
-- 
2.33.0

Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

head link

[PATCH 4/5] iommu/virtio: Pass end address to viommu_add_mapping()

To support identity mappings, the virtio-iommu driver must be able to
represent full 64-bit ranges internally. Pass (start, end) instead of
(start, size) to viommu_add/del_mapping().

Clean comments. The one about the returned size was never true: when
sweeping the whole address space the returned size will most certainly
be smaller than 2^64.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 drivers/iommu/virtio-iommu.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index d63ec4d11b00..eceb9281c8c1 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -311,8 +311,8 @@ static int viommu_send_req_sync(struct viommu_dev *viommu,
void *buf,
  *
  * On success, return the new mapping. Otherwise return NULL.
  */
-static int viommu_add_mapping(struct viommu_domain *vdomain, unsigned long
iova,
-			      phys_addr_t paddr, size_t size, u32 flags)
+static int viommu_add_mapping(struct viommu_domain *vdomain, u64 iova, u64 end,
+			      phys_addr_t paddr, u32 flags)
 {
 	unsigned long irqflags;
 	struct viommu_mapping *mapping;
@@ -323,7 +323,7 @@ static int viommu_add_mapping(struct viommu_domain *vdomain,
unsigned long iova,
 
 	mapping->paddr		= paddr;
 	mapping->iova.start	= iova;
-	mapping->iova.last	= iova + size - 1;
+	mapping->iova.last	= end;
 	mapping->flags		= flags;
 
 	spin_lock_irqsave(&vdomain->mappings_lock, irqflags);
@@ -338,26 +338,24 @@ static int viommu_add_mapping(struct viommu_domain
*vdomain, unsigned long iova,
  *
  * @vdomain: the domain
  * @iova: start of the range
- * @size: size of the range. A size of 0 corresponds to the entire address
- *	space.
+ * @end: end of the range
  *
- * On success, returns the number of unmapped bytes (>= size)
+ * On success, returns the number of unmapped bytes
  */
 static size_t viommu_del_mappings(struct viommu_domain *vdomain,
-				  unsigned long iova, size_t size)
+				  u64 iova, u64 end)
 {
 	size_t unmapped = 0;
 	unsigned long flags;
-	unsigned long last = iova + size - 1;
 	struct viommu_mapping *mapping = NULL;
 	struct interval_tree_node *node, *next;
 
 	spin_lock_irqsave(&vdomain->mappings_lock, flags);
-	next = interval_tree_iter_first(&vdomain->mappings, iova, last);
+	next = interval_tree_iter_first(&vdomain->mappings, iova, end);
 	while (next) {
 		node = next;
 		mapping = container_of(node, struct viommu_mapping, iova);
-		next = interval_tree_iter_next(node, iova, last);
+		next = interval_tree_iter_next(node, iova, end);
 
 		/* Trying to split a mapping? */
 		if (mapping->iova.start < iova)
@@ -656,8 +654,8 @@ static void viommu_domain_free(struct iommu_domain *domain)
 {
 	struct viommu_domain *vdomain = to_viommu_domain(domain);
 
-	/* Free all remaining mappings (size 2^64) */
-	viommu_del_mappings(vdomain, 0, 0);
+	/* Free all remaining mappings */
+	viommu_del_mappings(vdomain, 0, ULLONG_MAX);
 
 	if (vdomain->viommu)
 		ida_free(&vdomain->viommu->domain_ids, vdomain->id);
@@ -742,6 +740,7 @@ static int viommu_map(struct iommu_domain *domain, unsigned
long iova,
 {
 	int ret;
 	u32 flags;
+	u64 end = iova + size - 1;
 	struct virtio_iommu_req_map map;
 	struct viommu_domain *vdomain = to_viommu_domain(domain);
 
@@ -752,7 +751,7 @@ static int viommu_map(struct iommu_domain *domain, unsigned
long iova,
 	if (flags & ~vdomain->map_flags)
 		return -EINVAL;
 
-	ret = viommu_add_mapping(vdomain, iova, paddr, size, flags);
+	ret = viommu_add_mapping(vdomain, iova, end, paddr, flags);
 	if (ret)
 		return ret;
 
@@ -761,7 +760,7 @@ static int viommu_map(struct iommu_domain *domain, unsigned
long iova,
 		.domain		= cpu_to_le32(vdomain->id),
 		.virt_start	= cpu_to_le64(iova),
 		.phys_start	= cpu_to_le64(paddr),
-		.virt_end	= cpu_to_le64(iova + size - 1),
+		.virt_end	= cpu_to_le64(end),
 		.flags		= cpu_to_le32(flags),
 	};
 
@@ -770,7 +769,7 @@ static int viommu_map(struct iommu_domain *domain, unsigned
long iova,
 
 	ret = viommu_send_req_sync(vdomain->viommu, &map, sizeof(map));
 	if (ret)
-		viommu_del_mappings(vdomain, iova, size);
+		viommu_del_mappings(vdomain, iova, end);
 
 	return ret;
 }
@@ -783,7 +782,7 @@ static size_t viommu_unmap(struct iommu_domain *domain,
unsigned long iova,
 	struct virtio_iommu_req_unmap unmap;
 	struct viommu_domain *vdomain = to_viommu_domain(domain);
 
-	unmapped = viommu_del_mappings(vdomain, iova, size);
+	unmapped = viommu_del_mappings(vdomain, iova, iova + size - 1);
 	if (unmapped < size)
 		return 0;
 
-- 
2.33.0

Jean-Philippe Brucker

2021-Oct-13 12:10 UTC

head link

[PATCH 5/5] iommu/virtio: Support identity-mapped domains

Support identity domains for devices that do not offer the
VIRTIO_IOMMU_F_BYPASS_CONFIG feature, by creating 1:1 mappings between
the virtual and physical address space. Identity domains created this
way still perform noticeably better than DMA domains, because they don't
have the overhead of setting up and tearing down mappings at runtime.
The performance difference between this and bypass is minimal in
comparison.

It does not matter that the physical addresses in the identity mappings
do not all correspond to memory. By enabling passthrough we are trusting
the device driver and the device itself to only perform DMA to suitable
locations. In some cases it may even be desirable to perform DMA to MMIO
regions.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 drivers/iommu/virtio-iommu.c | 61 +++++++++++++++++++++++++++++++++---
 1 file changed, 57 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index eceb9281c8c1..c9e8367d2962 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -375,6 +375,55 @@ static size_t viommu_del_mappings(struct viommu_domain
*vdomain,
 	return unmapped;
 }
 
+/*
+ * Fill the domain with identity mappings, skipping the device's reserved
+ * regions.
+ */
+static int viommu_domain_map_identity(struct viommu_endpoint *vdev,
+				      struct viommu_domain *vdomain)
+{
+	int ret;
+	struct iommu_resv_region *resv;
+	u64 iova = vdomain->domain.geometry.aperture_start;
+	u64 limit = vdomain->domain.geometry.aperture_end;
+	u32 flags = VIRTIO_IOMMU_MAP_F_READ | VIRTIO_IOMMU_MAP_F_WRITE;
+	unsigned long granule = 1UL << __ffs(vdomain->domain.pgsize_bitmap);
+
+	iova = ALIGN(iova, granule);
+	limit = ALIGN_DOWN(limit + 1, granule) - 1;
+
+	list_for_each_entry(resv, &vdev->resv_regions, list) {
+		u64 resv_start = ALIGN_DOWN(resv->start, granule);
+		u64 resv_end = ALIGN(resv->start + resv->length, granule) - 1;
+
+		if (resv_end < iova || resv_start > limit)
+			/* No overlap */
+			continue;
+
+		if (resv_start > iova) {
+			ret = viommu_add_mapping(vdomain, iova, resv_start - 1,
+						 (phys_addr_t)iova, flags);
+			if (ret)
+				goto err_unmap;
+		}
+
+		if (resv_end >= limit)
+			return 0;
+
+		iova = resv_end + 1;
+	}
+
+	ret = viommu_add_mapping(vdomain, iova, limit, (phys_addr_t)iova,
+				 flags);
+	if (ret)
+		goto err_unmap;
+	return 0;
+
+err_unmap:
+	viommu_del_mappings(vdomain, 0, iova);
+	return ret;
+}
+
 /*
  * viommu_replay_mappings - re-send MAP requests
  *
@@ -637,14 +686,18 @@ static int viommu_domain_finalise(struct viommu_endpoint
*vdev,
 	vdomain->viommu		= viommu;
 
 	if (domain->type == IOMMU_DOMAIN_IDENTITY) {
-		if (!virtio_has_feature(viommu->vdev,
-					VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
+		if (virtio_has_feature(viommu->vdev,
+				       VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
+			vdomain->bypass = true;
+			return 0;
+		}
+
+		ret = viommu_domain_map_identity(vdev, vdomain);
+		if (ret) {
 			ida_free(&viommu->domain_ids, vdomain->id);
 			vdomain->viommu = 0;
 			return -EOPNOTSUPP;
 		}
-
-		vdomain->bypass = true;
 	}
 
 	return 0;
-- 
2.33.0

Tian, Kevin

2021-Oct-14 03:00 UTC

head link

[PATCH 0/5] iommu/virtio: Add identity domains

> From: Jean-Philippe Brucker <jean-philippe at linaro.org>
> Sent: Wednesday, October 13, 2021 8:11 PM
> 
> Support identity domains, allowing to only enable IOMMU protection for a
> subset of endpoints (those assigned to userspace, for example). Users
> may enable identity domains at compile time
> (CONFIG_IOMMU_DEFAULT_PASSTHROUGH), boot time
> (iommu.passthrough=1) or
> runtime (/sys/kernel/iommu_groups/*/type = identity).
Do we want to use consistent terms between spec (bypass domain) 
and code (identity domain)? 
> 
> Patches 1-2 support identity domains using the optional
> VIRTIO_IOMMU_F_BYPASS_CONFIG feature. The feature bit is not yet in the
> spec, see [1] for the latest proposal.
> 
> Patches 3-5 add a fallback to identity mappings, when the feature is not
> supported.
> 
> Note that this series doesn't touch the global bypass bit added by
> VIRTIO_IOMMU_F_BYPASS_CONFIG. All endpoints managed by the IOMMU
> should
> be attached to a domain, so global bypass isn't in use after endpoints
I saw a concept of deferred attach in iommu core. See iommu_is_
attach_deferred(). Currently this is vendor specific and I haven't
looked into the exact reason why some vendor sets it now. Just
be curious whether the same reason might be applied to virtio-iommu.
> are probed. Before that, the global bypass policy is decided by the
> hypervisor and firmware. So I don't think Linux needs to touch the
This reminds me one thing. The spec says that the global bypass
bit is sticky and not affected by reset. This implies that in the case
of rebooting the VM into a different OS, the previous OS actually
has the right to override this setting for the next OS. Is it a right
design? Even the firmware itself is unable to identify the original
setting enforced by the hypervisor after reboot. I feel the hypervisor
setting should be recovered after reset since it reflects the 
security measure enforced by the virtual platform?
> global bypass bit, but there are some patches available on my
> virtio-iommu/bypass branch [2] to test it.
> 
> QEMU patches are on my virtio-iommu/bypass branch [3] (and the list)
> 
> [1] https://www.mail-archive.com/virtio-dev at lists.oasis-
> open.org/msg07898.html
> [2] https://jpbrucker.net/git/linux/log/?h=virtio-iommu/bypass
> [3] https://jpbrucker.net/git/qemu/log/?h=virtio-iommu/bypass
> 
> Jean-Philippe Brucker (5):
>   iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG
>   iommu/virtio: Support bypass domains
>   iommu/virtio: Sort reserved regions
>   iommu/virtio: Pass end address to viommu_add_mapping()
>   iommu/virtio: Support identity-mapped domains
> 
>  include/uapi/linux/virtio_iommu.h |   8 ++-
>  drivers/iommu/virtio-iommu.c      | 113 +++++++++++++++++++++++++-----
>  2 files changed, 101 insertions(+), 20 deletions(-)
> 
> --
> 2.33.0

Tian, Kevin

2021-Oct-21 06:48 UTC

head link

[PATCH 0/5] iommu/virtio: Add identity domains

> From: Jean-Philippe Brucker <jean-philippe at linaro.org>
> Sent: Wednesday, October 13, 2021 8:11 PM
> 
> Support identity domains, allowing to only enable IOMMU protection for a
> subset of endpoints (those assigned to userspace, for example). Users
> may enable identity domains at compile time
> (CONFIG_IOMMU_DEFAULT_PASSTHROUGH), boot time
> (iommu.passthrough=1) or
> runtime (/sys/kernel/iommu_groups/*/type = identity).
> 
> Patches 1-2 support identity domains using the optional
> VIRTIO_IOMMU_F_BYPASS_CONFIG feature. The feature bit is not yet in the
> spec, see [1] for the latest proposal.
> 
> Patches 3-5 add a fallback to identity mappings, when the feature is not
> supported.
> 
> Note that this series doesn't touch the global bypass bit added by
> VIRTIO_IOMMU_F_BYPASS_CONFIG. All endpoints managed by the IOMMU
> should
> be attached to a domain, so global bypass isn't in use after endpoints
> are probed. Before that, the global bypass policy is decided by the
> hypervisor and firmware. So I don't think Linux needs to touch the
> global bypass bit, but there are some patches available on my
> virtio-iommu/bypass branch [2] to test it.
> 
> QEMU patches are on my virtio-iommu/bypass branch [3] (and the list)
> 
> [1] https://www.mail-archive.com/virtio-dev at lists.oasis-
> open.org/msg07898.html
> [2] https://jpbrucker.net/git/linux/log/?h=virtio-iommu/bypass
> [3] https://jpbrucker.net/git/qemu/log/?h=virtio-iommu/bypass
> 
> Jean-Philippe Brucker (5):
>   iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG
>   iommu/virtio: Support bypass domains
>   iommu/virtio: Sort reserved regions
>   iommu/virtio: Pass end address to viommu_add_mapping()
>   iommu/virtio: Support identity-mapped domains
> 
>  include/uapi/linux/virtio_iommu.h |   8 ++-
>  drivers/iommu/virtio-iommu.c      | 113 +++++++++++++++++++++++++-----
>  2 files changed, 101 insertions(+), 20 deletions(-)
> 
For this series:

	Reviewed-by: Kevin Tian <kevin.tian at intel.com>

Michael S. Tsirkin

2021-Oct-22 10:16 UTC

head link

[PATCH 0/5] iommu/virtio: Add identity domains

On Wed, Oct 13, 2021 at 01:10:48PM +0100, Jean-Philippe Brucker
wrote:> Support identity domains, allowing to only enable IOMMU protection for a
> subset of endpoints (those assigned to userspace, for example). Users
> may enable identity domains at compile time
> (CONFIG_IOMMU_DEFAULT_PASSTHROUGH), boot time (iommu.passthrough=1) or
> runtime (/sys/kernel/iommu_groups/*/type = identity).

I put this in my branch so it can get testing under linux-next,
but pls notice if the ballot does not conclude in time
for the merge window I won't send it to Linus.
> Patches 1-2 support identity domains using the optional
> VIRTIO_IOMMU_F_BYPASS_CONFIG feature. The feature bit is not yet in the
> spec, see [1] for the latest proposal.
> 
> Patches 3-5 add a fallback to identity mappings, when the feature is not
> supported.
> 
> Note that this series doesn't touch the global bypass bit added by
> VIRTIO_IOMMU_F_BYPASS_CONFIG. All endpoints managed by the IOMMU should
> be attached to a domain, so global bypass isn't in use after endpoints
> are probed. Before that, the global bypass policy is decided by the
> hypervisor and firmware. So I don't think Linux needs to touch the
> global bypass bit, but there are some patches available on my
> virtio-iommu/bypass branch [2] to test it.
> 
> QEMU patches are on my virtio-iommu/bypass branch [3] (and the list)
> 
> [1] https://www.mail-archive.com/virtio-dev at
lists.oasis-open.org/msg07898.html
> [2] https://jpbrucker.net/git/linux/log/?h=virtio-iommu/bypass
> [3] https://jpbrucker.net/git/qemu/log/?h=virtio-iommu/bypass
> 
> Jean-Philippe Brucker (5):
>   iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG
>   iommu/virtio: Support bypass domains
>   iommu/virtio: Sort reserved regions
>   iommu/virtio: Pass end address to viommu_add_mapping()
>   iommu/virtio: Support identity-mapped domains
> 
>  include/uapi/linux/virtio_iommu.h |   8 ++-
>  drivers/iommu/virtio-iommu.c      | 113 +++++++++++++++++++++++++-----
>  2 files changed, 101 insertions(+), 20 deletions(-)
> 
> -- 
> 2.33.0

Linux Virtualization - Oct 2021 - [PATCH 2/5] iommu/virtio: Support bypass domains

[PATCH 0/5] iommu/virtio: Add identity domains

[PATCH 1/5] iommu/virtio: Add definitions for VIRTIO_IOMMU_F_BYPASS_CONFIG

[PATCH 2/5] iommu/virtio: Support bypass domains

[PATCH 3/5] iommu/virtio: Sort reserved regions

[PATCH 4/5] iommu/virtio: Pass end address to viommu_add_mapping()

[PATCH 5/5] iommu/virtio: Support identity-mapped domains

[PATCH 0/5] iommu/virtio: Add identity domains

[PATCH 0/5] iommu/virtio: Add identity domains

[PATCH 0/5] iommu/virtio: Add identity domains