[PATCH v7 0/6] Add non-strict mode support for iommu-dma

[PATCH v7 0/6] Add non-strict mode support for iommu-dma

[Robin Murphy]

Hi all,

Since we'd like to get this polished up and merged and Leizhen has other
commitments, here's v7 of the previous series[1] wherein I address all
my own feedback :) This is a quick tweak of the v6 I sent yesterday
since I figured out slightly too late a much neater way of setting the
attribute at the appropriate time.

The principal change is that I've inverted things slightly such that
it's now a generic domain attribute controlled by iommu-dma given the
necessary support from individual IOMMU drivers. That way we can easily
enable other drivers straight away, as I've done for SMMUv2 here (which
also allowed me to give it a quick test with MMU-401s on a Juno board).
Otherwise it's really just cosmetic cleanup and rebasing onto Will's
pending SMMU queue.

Robin.

[1] https://www.mail-archive.com/iommu@lists.linux-foundation.org/msg25150.html


Robin Murphy (1):
  iommu/arm-smmu: Support non-strict mode

Zhen Lei (5):
  iommu/arm-smmu-v3: Implement flush_iotlb_all hook
  iommu/dma: Add support for non-strict mode
  iommu/io-pgtable-arm: Add support for non-strict mode
  iommu: Add bootup option "iommu.non_strict"
  iommu/arm-smmu-v3: Add support for non-strict mode

 .../admin-guide/kernel-parameters.txt         | 13 ++++++
 drivers/iommu/arm-smmu-v3.c                   | 40 +++++++++++++++----
 drivers/iommu/arm-smmu.c                      | 40 +++++++++++++++----
 drivers/iommu/dma-iommu.c                     | 29 +++++++++++++-
 drivers/iommu/io-pgtable-arm.c                |  9 +++--
 drivers/iommu/io-pgtable.h                    |  5 +++
 drivers/iommu/iommu.c                         | 26 ++++++++++++
 include/linux/iommu.h                         |  1 +
 8 files changed, 145 insertions(+), 18 deletions(-)

-- 
2.19.0.dirty

[PATCH v7 1/6] iommu/arm-smmu-v3: Implement flush_iotlb_all hook

[Robin Murphy]

From: Zhen Lei <thunder.leizhen@huawei.com>

.flush_iotlb_all is currently stubbed to arm_smmu_iotlb_sync() since the
only time it would ever need to actually do anything is for callers
doing their own explicit batching, e.g.:

	iommu_unmap_fast(domain, ...);
	iommu_unmap_fast(domain, ...);
	iommu_iotlb_flush_all(domain, ...);

where since io-pgtable still issues the TLBI commands implicitly in the
unmap instead of implementing .iotlb_range_add, the "flush" only needs
to ensure completion of those already-in-flight invalidations.

However, we're about to start using it in anger with flush queues, so
let's get a proper implementation wired up.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
[rm: expand commit message]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index e395f1ff3f81..f10c852479fc 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1781,6 +1781,14 @@ arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
 	return ops->unmap(ops, iova, size);
 }
 
+static void arm_smmu_flush_iotlb_all(struct iommu_domain *domain)
+{
+	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
+
+	if (smmu_domain->smmu)
+		arm_smmu_tlb_inv_context(smmu_domain);
+}
+
 static void arm_smmu_iotlb_sync(struct iommu_domain *domain)
 {
 	struct arm_smmu_device *smmu = to_smmu_domain(domain)->smmu;
@@ -2008,7 +2016,7 @@ static struct iommu_ops arm_smmu_ops = {
 	.attach_dev		= arm_smmu_attach_dev,
 	.map			= arm_smmu_map,
 	.unmap			= arm_smmu_unmap,
-	.flush_iotlb_all	= arm_smmu_iotlb_sync,
+	.flush_iotlb_all	= arm_smmu_flush_iotlb_all,
 	.iotlb_sync		= arm_smmu_iotlb_sync,
 	.iova_to_phys		= arm_smmu_iova_to_phys,
 	.add_device		= arm_smmu_add_device,
-- 
2.19.0.dirty

[PATCH v7 2/6] iommu/dma: Add support for non-strict mode

[Robin Murphy]

From: Zhen Lei <thunder.leizhen@huawei.com>

1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
   capable call domain->ops->flush_iotlb_all to flush TLB.
2. During the iommu domain initialization phase, base on domain->non_strict
   field to check whether non-strict mode is supported or not. If so, call
   init_iova_flush_queue to register iovad->flush_cb callback.
3. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
   -->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
   put off iova freeing, and omit iommu_tlb_sync operation.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: convert raw boolean to domain attribute]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/dma-iommu.c | 29 ++++++++++++++++++++++++++++-
 include/linux/iommu.h     |  1 +
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 511ff9a1d6d9..092e6926dc3c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -55,6 +55,9 @@ struct iommu_dma_cookie {
 	};
 	struct list_head		msi_page_list;
 	spinlock_t			msi_lock;
+
+	/* Only be assigned in non-strict mode, otherwise it's NULL */
+	struct iommu_domain		*domain;
 };
 
 static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
@@ -257,6 +260,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
 	return ret;
 }
 
+static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
+{
+	struct iommu_dma_cookie *cookie;
+	struct iommu_domain *domain;
+
+	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
+	domain = cookie->domain;
+
+	domain->ops->flush_iotlb_all(domain);
+}
+
 /**
  * iommu_dma_init_domain - Initialise a DMA mapping domain
  * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
@@ -275,6 +289,7 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
 	struct iova_domain *iovad = &cookie->iovad;
 	unsigned long order, base_pfn, end_pfn;
+	int attr = 1;
 
 	if (!cookie || cookie->type != IOMMU_DMA_IOVA_COOKIE)
 		return -EINVAL;
@@ -308,6 +323,13 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 	}
 
 	init_iova_domain(iovad, 1UL << order, base_pfn);
+
+	if (!iommu_domain_get_attr(domain, DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
+			&attr) && attr) {
+		cookie->domain = domain;
+		init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all, NULL);
+	}
+
 	if (!dev)
 		return 0;
 
@@ -393,6 +415,9 @@ static void iommu_dma_free_iova(struct iommu_dma_cookie *cookie,
 	/* The MSI case is only ever cleaning up its most recent allocation */
 	if (cookie->type == IOMMU_DMA_MSI_COOKIE)
 		cookie->msi_iova -= size;
+	else if (cookie->domain)	/* non-strict mode */
+		queue_iova(iovad, iova_pfn(iovad, iova),
+				size >> iova_shift(iovad), 0);
 	else
 		free_iova_fast(iovad, iova_pfn(iovad, iova),
 				size >> iova_shift(iovad));
@@ -408,7 +433,9 @@ static void __iommu_dma_unmap(struct iommu_domain *domain, dma_addr_t dma_addr,
 	dma_addr -= iova_off;
 	size = iova_align(iovad, size + iova_off);
 
-	WARN_ON(iommu_unmap(domain, dma_addr, size) != size);
+	WARN_ON(iommu_unmap_fast(domain, dma_addr, size) != size);
+	if (!cookie->domain)
+		iommu_tlb_sync(domain);
 	iommu_dma_free_iova(cookie, dma_addr, size);
 }
 
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 87994c265bf5..decabe8e8dbe 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -124,6 +124,7 @@ enum iommu_attr {
 	DOMAIN_ATTR_FSL_PAMU_ENABLE,
 	DOMAIN_ATTR_FSL_PAMUV1,
 	DOMAIN_ATTR_NESTING,	/* two stages of translation */
+	DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
 	DOMAIN_ATTR_MAX,
 };
 
-- 
2.19.0.dirty

[PATCH v7 3/6] iommu/io-pgtable-arm: Add support for non-strict mode

[Robin Murphy]

From: Zhen Lei <thunder.leizhen@huawei.com>

To support non-strict mode, now we only TLBI and sync for strict mode,
except for non-leaf invalidations since page table updates themselves
must always be synchronous.

To save having to reason about it too much, make sure the invalidation
in arm_lpae_split_blk_unmap() just performs its own unconditional sync
to minimise the window in which we're technically violating the break-
before-make requirement on a live mapping. This might work out redundant
with an outer-level sync for strict unmaps, but we'll never be splitting
blocks on a DMA fastpath anyway.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: tweak comment, commit message, and split_blk_unmap logic]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/io-pgtable-arm.c | 9 ++++++---
 drivers/iommu/io-pgtable.h     | 5 +++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 2f79efd16a05..5b915aab7fd3 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -576,6 +576,7 @@ static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
 		tablep = iopte_deref(pte, data);
 	} else if (unmap_idx >= 0) {
 		io_pgtable_tlb_add_flush(&data->iop, iova, size, size, true);
+		io_pgtable_tlb_sync(&data->iop);
 		return size;
 	}
 
@@ -609,7 +610,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 			io_pgtable_tlb_sync(iop);
 			ptep = iopte_deref(pte, data);
 			__arm_lpae_free_pgtable(data, lvl + 1, ptep);
-		} else {
+		} else if (!(iop->cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT)) {
 			io_pgtable_tlb_add_flush(iop, iova, size, size, true);
 		}
 
@@ -771,7 +772,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
 	u64 reg;
 	struct arm_lpae_io_pgtable *data;
 
-	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS | IO_PGTABLE_QUIRK_NO_DMA))
+	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS | IO_PGTABLE_QUIRK_NO_DMA |
+			    IO_PGTABLE_QUIRK_NON_STRICT))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
@@ -863,7 +865,8 @@ arm_64_lpae_alloc_pgtable_s2(struct io_pgtable_cfg *cfg, void *cookie)
 	struct arm_lpae_io_pgtable *data;
 
 	/* The NS quirk doesn't apply at stage 2 */
-	if (cfg->quirks & ~IO_PGTABLE_QUIRK_NO_DMA)
+	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_NO_DMA |
+			    IO_PGTABLE_QUIRK_NON_STRICT))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
index 2df79093cad9..47d5ae559329 100644
--- a/drivers/iommu/io-pgtable.h
+++ b/drivers/iommu/io-pgtable.h
@@ -71,12 +71,17 @@ struct io_pgtable_cfg {
 	 *	be accessed by a fully cache-coherent IOMMU or CPU (e.g. for a
 	 *	software-emulated IOMMU), such that pagetable updates need not
 	 *	be treated as explicit DMA data.
+	 *
+	 * IO_PGTABLE_QUIRK_NON_STRICT: Skip issuing synchronous leaf TLBIs
+	 *	on unmap, for DMA domains using the flush queue mechanism for
+	 *	delayed invalidation.
 	 */
 	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
 	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
 	#define IO_PGTABLE_QUIRK_TLBI_ON_MAP	BIT(2)
 	#define IO_PGTABLE_QUIRK_ARM_MTK_4GB	BIT(3)
 	#define IO_PGTABLE_QUIRK_NO_DMA		BIT(4)
+	#define IO_PGTABLE_QUIRK_NON_STRICT	BIT(5)
 	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;
-- 
2.19.0.dirty

[PATCH v7 4/6] iommu: Add bootup option "iommu.non_strict"

[Robin Murphy]

From: Zhen Lei <thunder.leizhen@huawei.com>

Add a bootup option to make the system manager can choose which mode to
be used. The default mode is strict.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: move handling out of SMMUv3 driver]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 .../admin-guide/kernel-parameters.txt         | 13 ++++++++++
 drivers/iommu/iommu.c                         | 26 +++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..406b91759b62 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1749,6 +1749,19 @@
 		nobypass	[PPC/POWERNV]
 			Disable IOMMU bypass, using IOMMU for PCI devices.
 
+	iommu.non_strict=	[ARM64]
+			Format: { "0" | "1" }
+			0 - strict mode, default.
+			    Release IOVAs after the related TLBs are invalid
+			    completely.
+			1 - non-strict mode.
+			    Put off TLBs invalidation and release memory first.
+			    It's good for scatter-gather performance but lacks
+			    full isolation, an untrusted device can access the
+			    reused memory because the TLBs may still valid.
+			    Please take	full consideration before choosing this
+			    mode. Note that, VFIO will always use strict mode.
+
 	iommu.passthrough=
 			[ARM64] Configure DMA to bypass the IOMMU by default.
 			Format: { "0" | "1" }
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8c15c5980299..2cabd0c0a4f3 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -41,6 +41,7 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
 #else
 static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
 #endif
+static bool iommu_dma_non_strict __read_mostly;
 
 struct iommu_callback_data {
 	const struct iommu_ops *ops;
@@ -131,6 +132,24 @@ static int __init iommu_set_def_domain_type(char *str)
 }
 early_param("iommu.passthrough", iommu_set_def_domain_type);
 
+static int __init iommu_dma_setup(char *str)
+{
+	int ret;
+
+	ret = kstrtobool(str, &iommu_dma_non_strict);
+	if (ret)
+		return ret;
+
+	if (iommu_dma_non_strict) {
+		pr_warn("WARNING: iommu non-strict mode is chosen.\n"
+			"It's good for scatter-gather performance but lacks full isolation\n");
+		add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
+	}
+
+	return 0;
+}
+early_param("iommu.non_strict", iommu_dma_setup);
+
 static ssize_t iommu_group_attr_show(struct kobject *kobj,
 				     struct attribute *__attr, char *buf)
 {
@@ -1072,6 +1091,13 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 		group->default_domain = dom;
 		if (!group->domain)
 			group->domain = dom;
+
+		if (dom && iommu_dma_non_strict) {
+			int attr = 1;
+			iommu_domain_set_attr(dom,
+					      DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
+					      &attr);
+		}
 	}
 
 	ret = iommu_group_add_device(group, dev);
-- 
2.19.0.dirty

[PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

[Robin Murphy]

From: Zhen Lei <thunder.leizhen@huawei.com>

Dynamically choose strict or non-strict mode for page table config based
on the iommu domain type.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: convert to domain attribute]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index f10c852479fc..7bbfa5f7ce8e 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -612,6 +612,7 @@ struct arm_smmu_domain {
 	struct mutex			init_mutex; /* Protects smmu pointer */
 
 	struct io_pgtable_ops		*pgtbl_ops;
+	bool				non_strict;
 
 	enum arm_smmu_domain_stage	stage;
 	union {
@@ -1633,6 +1634,9 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
 	if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
 		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
 
+	if (smmu_domain->non_strict)
+		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
+
 	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
 	if (!pgtbl_ops)
 		return -ENOMEM;
@@ -1934,13 +1938,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
 {
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
-		return -EINVAL;
-
 	switch (attr) {
 	case DOMAIN_ATTR_NESTING:
+		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
+			return -EINVAL;
 		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
 		return 0;
+	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
+		if (domain->type != IOMMU_DOMAIN_DMA)
+			return -EINVAL;
+		*(int *)data = smmu_domain->non_strict;
+		return 0;
 	default:
 		return -ENODEV;
 	}
@@ -1952,13 +1960,15 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 	int ret = 0;
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
-		return -EINVAL;
-
 	mutex_lock(&smmu_domain->init_mutex);
 
 	switch (attr) {
 	case DOMAIN_ATTR_NESTING:
+		if (domain->type != IOMMU_DOMAIN_UNMANAGED) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
 		if (smmu_domain->smmu) {
 			ret = -EPERM;
 			goto out_unlock;
@@ -1969,6 +1979,14 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 		else
 			smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
 
+		break;
+	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
+		if (domain->type != IOMMU_DOMAIN_DMA) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		smmu_domain->non_strict = *(int *)data;
 		break;
 	default:
 		ret = -ENODEV;
-- 
2.19.0.dirty

[PATCH v7 6/6] iommu/arm-smmu: Support non-strict mode

[Robin Murphy]

All we need is to wire up .flush_iotlb_all properly and implement the
domain attribute, and iommu-dma and io-pgtable-arm will do the rest for
us. Rather than bother implementing it for v7s format for the highly
unlikely chance of that being relevant, we can simply hide the
non-strict flag from io-pgtable for that combination just so anyone who
does actually try it will simply get over-invalidation instead of
failure to initialise domains.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu.c | 40 +++++++++++++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index fd1b80ef9490..aa5be334753b 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -246,6 +246,7 @@ struct arm_smmu_domain {
 	const struct iommu_gather_ops	*tlb_ops;
 	struct arm_smmu_cfg		cfg;
 	enum arm_smmu_domain_stage	stage;
+	bool				non_strict;
 	struct mutex			init_mutex; /* Protects smmu pointer */
 	spinlock_t			cb_lock; /* Serialises ATS1* ops and TLB syncs */
 	struct iommu_domain		domain;
@@ -863,6 +864,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 	if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK)
 		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
 
+	if (smmu_domain->non_strict && cfg->fmt != ARM_SMMU_CTX_FMT_AARCH32_S)
+		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
+
 	smmu_domain->smmu = smmu;
 	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
 	if (!pgtbl_ops) {
@@ -1252,6 +1256,14 @@ static size_t arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
 	return ops->unmap(ops, iova, size);
 }
 
+static void arm_smmu_flush_iotlb_all(struct iommu_domain *domain)
+{
+	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
+
+	if (smmu_domain->tlb_ops)
+		smmu_domain->tlb_ops->tlb_flush_all(smmu_domain);
+}
+
 static void arm_smmu_iotlb_sync(struct iommu_domain *domain)
 {
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
@@ -1470,13 +1482,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
 {
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
-		return -EINVAL;
-
 	switch (attr) {
 	case DOMAIN_ATTR_NESTING:
+		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
+			return -EINVAL;
 		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
 		return 0;
+	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
+		if (domain->type != IOMMU_DOMAIN_DMA)
+			return -EINVAL;
+		*(int *)data = smmu_domain->non_strict;
+		return 0;
 	default:
 		return -ENODEV;
 	}
@@ -1488,13 +1504,15 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 	int ret = 0;
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
-		return -EINVAL;
-
 	mutex_lock(&smmu_domain->init_mutex);
 
 	switch (attr) {
 	case DOMAIN_ATTR_NESTING:
+		if (domain->type != IOMMU_DOMAIN_UNMANAGED) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
 		if (smmu_domain->smmu) {
 			ret = -EPERM;
 			goto out_unlock;
@@ -1505,6 +1523,14 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 		else
 			smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
 
+		break;
+	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
+		if (domain->type != IOMMU_DOMAIN_DMA) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		smmu_domain->non_strict = *(int *)data;
 		break;
 	default:
 		ret = -ENODEV;
@@ -1562,7 +1588,7 @@ static struct iommu_ops arm_smmu_ops = {
 	.attach_dev		= arm_smmu_attach_dev,
 	.map			= arm_smmu_map,
 	.unmap			= arm_smmu_unmap,
-	.flush_iotlb_all	= arm_smmu_iotlb_sync,
+	.flush_iotlb_all	= arm_smmu_flush_iotlb_all,
 	.iotlb_sync		= arm_smmu_iotlb_sync,
 	.iova_to_phys		= arm_smmu_iova_to_phys,
 	.add_device		= arm_smmu_add_device,
-- 
2.19.0.dirty

Re: [PATCH v7 0/6] Add non-strict mode support for iommu-dma

[Will Deacon]

Hi Robin,

Thanks for turning this around so quickly.

On Fri, Sep 14, 2018 at 03:30:18PM +0100, Robin Murphy wrote:
> Since we'd like to get this polished up and merged and Leizhen has other
> commitments, here's v7 of the previous series[1] wherein I address all
> my own feedback :) This is a quick tweak of the v6 I sent yesterday
> since I figured out slightly too late a much neater way of setting the
> attribute at the appropriate time.
> 
> The principal change is that I've inverted things slightly such that
> it's now a generic domain attribute controlled by iommu-dma given the
> necessary support from individual IOMMU drivers. That way we can easily
> enable other drivers straight away, as I've done for SMMUv2 here (which
> also allowed me to give it a quick test with MMU-401s on a Juno board).
> Otherwise it's really just cosmetic cleanup and rebasing onto Will's
> pending SMMU queue.

I've been through and had a look, leaving some small comments on the patches
themselves. The only part I failed to figure out is how you tie the lifetime
of the flush queue to the lifetime of the domain so that the timer callback
can't fire after e.g. the DMA cookie has been freed. How does that work?

Cheers,

Will

Re: [PATCH v7 2/6] iommu/dma: Add support for non-strict mode

[Will Deacon]

Hi Robin,

On Fri, Sep 14, 2018 at 03:30:20PM +0100, Robin Murphy wrote:
> From: Zhen Lei <thunder.leizhen@huawei.com>
> 
> 1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
>    capable call domain->ops->flush_iotlb_all to flush TLB.
> 2. During the iommu domain initialization phase, base on domain->non_strict
>    field to check whether non-strict mode is supported or not. If so, call
>    init_iova_flush_queue to register iovad->flush_cb callback.
> 3. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
>    -->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
>    put off iova freeing, and omit iommu_tlb_sync operation.

Hmm, this is basically just a commentary on the code. Please could you write
it more in terms of the problem that's being solved?

> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> [rm: convert raw boolean to domain attribute]
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/dma-iommu.c | 29 ++++++++++++++++++++++++++++-
>  include/linux/iommu.h     |  1 +
>  2 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 511ff9a1d6d9..092e6926dc3c 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -55,6 +55,9 @@ struct iommu_dma_cookie {
>  	};
>  	struct list_head		msi_page_list;
>  	spinlock_t			msi_lock;
> +
> +	/* Only be assigned in non-strict mode, otherwise it's NULL */
> +	struct iommu_domain		*domain;
>  };
>  
>  static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
> @@ -257,6 +260,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
>  	return ret;
>  }
>  
> +static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
> +{
> +	struct iommu_dma_cookie *cookie;
> +	struct iommu_domain *domain;
> +
> +	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
> +	domain = cookie->domain;
> +
> +	domain->ops->flush_iotlb_all(domain);

Can we rely on this function pointer being non-NULL? I think it would
be better to call iommu_flush_tlb_all(cookie->domain) instead.

> +}
> +
>  /**
>   * iommu_dma_init_domain - Initialise a DMA mapping domain
>   * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
> @@ -275,6 +289,7 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>  	struct iommu_dma_cookie *cookie = domain->iova_cookie;
>  	struct iova_domain *iovad = &cookie->iovad;
>  	unsigned long order, base_pfn, end_pfn;
> +	int attr = 1;

Do we actually need to initialise this?

Will

Re: [PATCH v7 4/6] iommu: Add bootup option "iommu.non_strict"

[Will Deacon]

On Fri, Sep 14, 2018 at 03:30:22PM +0100, Robin Murphy wrote:
> From: Zhen Lei <thunder.leizhen@huawei.com>
> 
> Add a bootup option to make the system manager can choose which mode to
> be used. The default mode is strict.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> [rm: move handling out of SMMUv3 driver]
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  .../admin-guide/kernel-parameters.txt         | 13 ++++++++++
>  drivers/iommu/iommu.c                         | 26 +++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 9871e649ffef..406b91759b62 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1749,6 +1749,19 @@
>  		nobypass	[PPC/POWERNV]
>  			Disable IOMMU bypass, using IOMMU for PCI devices.
>  
> +	iommu.non_strict=	[ARM64]
> +			Format: { "0" | "1" }
> +			0 - strict mode, default.
> +			    Release IOVAs after the related TLBs are invalid
> +			    completely.
> +			1 - non-strict mode.
> +			    Put off TLBs invalidation and release memory first.
> +			    It's good for scatter-gather performance but lacks
> +			    full isolation, an untrusted device can access the
> +			    reused memory because the TLBs may still valid.
> +			    Please take	full consideration before choosing this
> +			    mode. Note that, VFIO will always use strict mode.

This text needs help. How about something like:

	0 - strict mode, default.
	    Invalidate the TLB of the IOMMU hardware as part of every
	    unmap() operation.
	1 - lazy mode.
	    Defer TLB invalidation so that the TLB of the IOMMU hardware
	    is invalidated periodically, rather than as part of every
	    unmap() operation.

(generally, I think I'd s/non strict/lazy/ in this patch to avoid the double
negatives)

> +
>  	iommu.passthrough=
>  			[ARM64] Configure DMA to bypass the IOMMU by default.
>  			Format: { "0" | "1" }
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 8c15c5980299..2cabd0c0a4f3 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -41,6 +41,7 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
>  #else
>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>  #endif
> +static bool iommu_dma_non_strict __read_mostly;
>  
>  struct iommu_callback_data {
>  	const struct iommu_ops *ops;
> @@ -131,6 +132,24 @@ static int __init iommu_set_def_domain_type(char *str)
>  }
>  early_param("iommu.passthrough", iommu_set_def_domain_type);
>  
> +static int __init iommu_dma_setup(char *str)
> +{
> +	int ret;
> +
> +	ret = kstrtobool(str, &iommu_dma_non_strict);
> +	if (ret)
> +		return ret;
> +
> +	if (iommu_dma_non_strict) {
> +		pr_warn("WARNING: iommu non-strict mode is chosen.\n"
> +			"It's good for scatter-gather performance but lacks full isolation\n");

Hmm, not sure about this message either and tainting is probably over the
top. Maybe drop the taint and just pr_info something like "IOMMU DMA ops
using lazy TLB invalidation: unable to protect against malicious devices"

> +		add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
> +	}
> +
> +	return 0;
> +}
> +early_param("iommu.non_strict", iommu_dma_setup);
> +
>  static ssize_t iommu_group_attr_show(struct kobject *kobj,
>  				     struct attribute *__attr, char *buf)
>  {
> @@ -1072,6 +1091,13 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
>  		group->default_domain = dom;
>  		if (!group->domain)
>  			group->domain = dom;
> +
> +		if (dom && iommu_dma_non_strict) {
> +			int attr = 1;
> +			iommu_domain_set_attr(dom,
> +					      DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
> +					      &attr);
> +		}

Hmm, I don't think we can guarantee that we're working with the DMA domain
here. Does this all fall out in the wash for the identity domain?

Will

Re: [PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

[Will Deacon]

On Fri, Sep 14, 2018 at 03:30:23PM +0100, Robin Murphy wrote:
> From: Zhen Lei <thunder.leizhen@huawei.com>
> 
> Dynamically choose strict or non-strict mode for page table config based
> on the iommu domain type.

It's the domain type in conjunction with the attribute that determines
whether we use lazy or strict invalidation.

> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> [rm: convert to domain attribute]
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 30 ++++++++++++++++++++++++------
>  1 file changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index f10c852479fc..7bbfa5f7ce8e 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -612,6 +612,7 @@ struct arm_smmu_domain {
>  	struct mutex			init_mutex; /* Protects smmu pointer */
>  
>  	struct io_pgtable_ops		*pgtbl_ops;
> +	bool				non_strict;
>  
>  	enum arm_smmu_domain_stage	stage;
>  	union {
> @@ -1633,6 +1634,9 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
>  	if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
>  		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>  
> +	if (smmu_domain->non_strict)
> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> +
>  	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>  	if (!pgtbl_ops)
>  		return -ENOMEM;
> @@ -1934,13 +1938,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>  {
>  	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>  
> -	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
> -		return -EINVAL;
> -
>  	switch (attr) {
>  	case DOMAIN_ATTR_NESTING:
> +		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
> +			return -EINVAL;
>  		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>  		return 0;
> +	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
> +		if (domain->type != IOMMU_DOMAIN_DMA)
> +			return -EINVAL;
> +		*(int *)data = smmu_domain->non_strict;
> +		return 0;
>  	default:
>  		return -ENODEV;

Hmm, there's a change in behaviour here (and also in the set function)
which is that unknown attributes now return -ENODEV for managed domains
instead of -EINVAL. I don't know if that's a problem, but I'd be inclined
to switch on the domain type and then have a nested switch for the supported
attributes.

Will

Re: [PATCH v7 6/6] iommu/arm-smmu: Support non-strict mode

[Will Deacon]

On Fri, Sep 14, 2018 at 03:30:24PM +0100, Robin Murphy wrote:
> All we need is to wire up .flush_iotlb_all properly and implement the
> domain attribute, and iommu-dma and io-pgtable-arm will do the rest for
> us. Rather than bother implementing it for v7s format for the highly
> unlikely chance of that being relevant, we can simply hide the
> non-strict flag from io-pgtable for that combination just so anyone who
> does actually try it will simply get over-invalidation instead of
> failure to initialise domains.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu.c | 40 +++++++++++++++++++++++++++++++++-------
>  1 file changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index fd1b80ef9490..aa5be334753b 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -246,6 +246,7 @@ struct arm_smmu_domain {
>  	const struct iommu_gather_ops	*tlb_ops;
>  	struct arm_smmu_cfg		cfg;
>  	enum arm_smmu_domain_stage	stage;
> +	bool				non_strict;
>  	struct mutex			init_mutex; /* Protects smmu pointer */
>  	spinlock_t			cb_lock; /* Serialises ATS1* ops and TLB syncs */
>  	struct iommu_domain		domain;
> @@ -863,6 +864,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  	if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK)
>  		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>  
> +	if (smmu_domain->non_strict && cfg->fmt != ARM_SMMU_CTX_FMT_AARCH32_S)
> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;

Does this mean we end up over-invalidating when using short-descriptor?
Could we not bypass the flush queue in this case instead? Ideally, we'd
just reject the domain attribute but I don't know if we know about the
page-table format early enough for that. Alternatively, we could force
long format if the attribute is set.

What do you think?

Will

Re: [PATCH v7 0/6] Add non-strict mode support for iommu-dma

[Robin Murphy]

Hi Will,

On 2018-09-18 6:10 PM, Will Deacon wrote:
> Hi Robin,
> 
> Thanks for turning this around so quickly.

Cheers for a pretty rapid review too :)

> On Fri, Sep 14, 2018 at 03:30:18PM +0100, Robin Murphy wrote:
>> Since we'd like to get this polished up and merged and Leizhen has other
>> commitments, here's v7 of the previous series[1] wherein I address all
>> my own feedback :) This is a quick tweak of the v6 I sent yesterday
>> since I figured out slightly too late a much neater way of setting the
>> attribute at the appropriate time.
>>
>> The principal change is that I've inverted things slightly such that
>> it's now a generic domain attribute controlled by iommu-dma given the
>> necessary support from individual IOMMU drivers. That way we can easily
>> enable other drivers straight away, as I've done for SMMUv2 here (which
>> also allowed me to give it a quick test with MMU-401s on a Juno board).
>> Otherwise it's really just cosmetic cleanup and rebasing onto Will's
>> pending SMMU queue.
> 
> I've been through and had a look, leaving some small comments on the patches
> themselves. The only part I failed to figure out is how you tie the lifetime
> of the flush queue to the lifetime of the domain so that the timer callback
> can't fire after e.g. the DMA cookie has been freed. How does that work?

Er, to be honest I haven't looked or even considered it! Other than the 
parts I've massaged I kinda took the functionality of the previous 
series for granted. Let me cross-check the x86 code and figure it out.

Robin.

Re: [PATCH v7 2/6] iommu/dma: Add support for non-strict mode

[Robin Murphy]

On 2018-09-18 6:10 PM, Will Deacon wrote:
> Hi Robin,
> 
> On Fri, Sep 14, 2018 at 03:30:20PM +0100, Robin Murphy wrote:
>> From: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> 1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
>>     capable call domain->ops->flush_iotlb_all to flush TLB.
>> 2. During the iommu domain initialization phase, base on domain->non_strict
>>     field to check whether non-strict mode is supported or not. If so, call
>>     init_iova_flush_queue to register iovad->flush_cb callback.
>> 3. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
>>     -->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
>>     put off iova freeing, and omit iommu_tlb_sync operation.
> 
> Hmm, this is basically just a commentary on the code. Please could you write
> it more in terms of the problem that's being solved?

Sure - I intentionally kept a light touch when it came to the 
documentation and commit messages in this rework (other than patch #1 
where I eventually remembered the original reasoning and that it wasn't 
a bug). If we're more-or-less happy with the shape of the technical side 
I'll make sure to take a final pass through v8 to tidy up all the prose.

>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> [rm: convert raw boolean to domain attribute]
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   drivers/iommu/dma-iommu.c | 29 ++++++++++++++++++++++++++++-
>>   include/linux/iommu.h     |  1 +
>>   2 files changed, 29 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index 511ff9a1d6d9..092e6926dc3c 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -55,6 +55,9 @@ struct iommu_dma_cookie {
>>   	};
>>   	struct list_head		msi_page_list;
>>   	spinlock_t			msi_lock;
>> +
>> +	/* Only be assigned in non-strict mode, otherwise it's NULL */
>> +	struct iommu_domain		*domain;
>>   };
>>   
>>   static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
>> @@ -257,6 +260,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
>>   	return ret;
>>   }
>>   
>> +static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
>> +{
>> +	struct iommu_dma_cookie *cookie;
>> +	struct iommu_domain *domain;
>> +
>> +	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
>> +	domain = cookie->domain;
>> +
>> +	domain->ops->flush_iotlb_all(domain);
> 
> Can we rely on this function pointer being non-NULL? I think it would
> be better to call iommu_flush_tlb_all(cookie->domain) instead.

Yeah, that's deliberate - in fact got as far as writing that change, 
then undid it as I realised that although the attribute conversion got 
rid of the explicit ops->flush_iotlb_all check, it still makes zero 
sense for an IOMMU driver to claim to support the flush queue attribute 
without also providing the relevant callback, so I do actually want this 
to blow up rather than silently do nothing if that assumption isn't met.

>> +}
>> +
>>   /**
>>    * iommu_dma_init_domain - Initialise a DMA mapping domain
>>    * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
>> @@ -275,6 +289,7 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>>   	struct iommu_dma_cookie *cookie = domain->iova_cookie;
>>   	struct iova_domain *iovad = &cookie->iovad;
>>   	unsigned long order, base_pfn, end_pfn;
>> +	int attr = 1;
> 
> Do we actually need to initialise this?

Oops, no, that's a left-over from the turned-out-messier-that-I-thought 
v6 implementation.

Thanks,
Robin.

Re: [PATCH v7 4/6] iommu: Add bootup option "iommu.non_strict"

[Robin Murphy]

On 2018-09-18 6:10 PM, Will Deacon wrote:
> On Fri, Sep 14, 2018 at 03:30:22PM +0100, Robin Murphy wrote:
>> From: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> Add a bootup option to make the system manager can choose which mode to
>> be used. The default mode is strict.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> [rm: move handling out of SMMUv3 driver]
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   .../admin-guide/kernel-parameters.txt         | 13 ++++++++++
>>   drivers/iommu/iommu.c                         | 26 +++++++++++++++++++
>>   2 files changed, 39 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 9871e649ffef..406b91759b62 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1749,6 +1749,19 @@
>>   		nobypass	[PPC/POWERNV]
>>   			Disable IOMMU bypass, using IOMMU for PCI devices.
>>   
>> +	iommu.non_strict=	[ARM64]
>> +			Format: { "0" | "1" }
>> +			0 - strict mode, default.
>> +			    Release IOVAs after the related TLBs are invalid
>> +			    completely.
>> +			1 - non-strict mode.
>> +			    Put off TLBs invalidation and release memory first.
>> +			    It's good for scatter-gather performance but lacks
>> +			    full isolation, an untrusted device can access the
>> +			    reused memory because the TLBs may still valid.
>> +			    Please take	full consideration before choosing this
>> +			    mode. Note that, VFIO will always use strict mode.
> 
> This text needs help. How about something like:
> 
> 	0 - strict mode, default.
> 	    Invalidate the TLB of the IOMMU hardware as part of every
> 	    unmap() operation.
> 	1 - lazy mode.
> 	    Defer TLB invalidation so that the TLB of the IOMMU hardware
> 	    is invalidated periodically, rather than as part of every
> 	    unmap() operation.
> 
> (generally, I think I'd s/non strict/lazy/ in this patch to avoid the double
> negatives)
> 
>> +
>>   	iommu.passthrough=
>>   			[ARM64] Configure DMA to bypass the IOMMU by default.
>>   			Format: { "0" | "1" }
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 8c15c5980299..2cabd0c0a4f3 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -41,6 +41,7 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
>>   #else
>>   static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>>   #endif
>> +static bool iommu_dma_non_strict __read_mostly;
>>   
>>   struct iommu_callback_data {
>>   	const struct iommu_ops *ops;
>> @@ -131,6 +132,24 @@ static int __init iommu_set_def_domain_type(char *str)
>>   }
>>   early_param("iommu.passthrough", iommu_set_def_domain_type);
>>   
>> +static int __init iommu_dma_setup(char *str)
>> +{
>> +	int ret;
>> +
>> +	ret = kstrtobool(str, &iommu_dma_non_strict);
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (iommu_dma_non_strict) {
>> +		pr_warn("WARNING: iommu non-strict mode is chosen.\n"
>> +			"It's good for scatter-gather performance but lacks full isolation\n");
> 
> Hmm, not sure about this message either and tainting is probably over the
> top. Maybe drop the taint and just pr_info something like "IOMMU DMA ops
> using lazy TLB invalidation: unable to protect against malicious devices"
> 
>> +		add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
>> +	}
>> +
>> +	return 0;
>> +}
>> +early_param("iommu.non_strict", iommu_dma_setup);
>> +
>>   static ssize_t iommu_group_attr_show(struct kobject *kobj,
>>   				     struct attribute *__attr, char *buf)
>>   {
>> @@ -1072,6 +1091,13 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
>>   		group->default_domain = dom;
>>   		if (!group->domain)
>>   			group->domain = dom;
>> +
>> +		if (dom && iommu_dma_non_strict) {
>> +			int attr = 1;
>> +			iommu_domain_set_attr(dom,
>> +					      DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
>> +					      &attr);
>> +		}
> 
> Hmm, I don't think we can guarantee that we're working with the DMA domain
> here. Does this all fall out in the wash for the identity domain?

Indeed so - for one, I expect drivers to reject it for anything that 
isn't their own default DMA ops domain type (as #5 and #6 do), and 
furthermore it only has any effect once iommu_dma_init_domain() reads it 
back if it stuck, and other domain types should never be getting passed 
into there anyway.

Robin.

Re: [PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

[Robin Murphy]

On 2018-09-18 6:10 PM, Will Deacon wrote:
> On Fri, Sep 14, 2018 at 03:30:23PM +0100, Robin Murphy wrote:
>> From: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> Dynamically choose strict or non-strict mode for page table config based
>> on the iommu domain type.
> 
> It's the domain type in conjunction with the attribute that determines
> whether we use lazy or strict invalidation.
> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> [rm: convert to domain attribute]
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   drivers/iommu/arm-smmu-v3.c | 30 ++++++++++++++++++++++++------
>>   1 file changed, 24 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index f10c852479fc..7bbfa5f7ce8e 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -612,6 +612,7 @@ struct arm_smmu_domain {
>>   	struct mutex			init_mutex; /* Protects smmu pointer */
>>   
>>   	struct io_pgtable_ops		*pgtbl_ops;
>> +	bool				non_strict;
>>   
>>   	enum arm_smmu_domain_stage	stage;
>>   	union {
>> @@ -1633,6 +1634,9 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
>>   	if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
>>   		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>>   
>> +	if (smmu_domain->non_strict)
>> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>> +
>>   	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>>   	if (!pgtbl_ops)
>>   		return -ENOMEM;
>> @@ -1934,13 +1938,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>>   {
>>   	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>   
>> -	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
>> -		return -EINVAL;
>> -
>>   	switch (attr) {
>>   	case DOMAIN_ATTR_NESTING:
>> +		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
>> +			return -EINVAL;
>>   		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>>   		return 0;
>> +	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
>> +		if (domain->type != IOMMU_DOMAIN_DMA)
>> +			return -EINVAL;
>> +		*(int *)data = smmu_domain->non_strict;
>> +		return 0;
>>   	default:
>>   		return -ENODEV;
> 
> Hmm, there's a change in behaviour here (and also in the set function)
> which is that unknown attributes now return -ENODEV for managed domains
> instead of -EINVAL. I don't know if that's a problem, but I'd be inclined
> to switch on the domain type and then have a nested switch for the supported
> attributes.

Sure, a nested switch did actually cross my mind, but I was worried it 
might be a little boilerplate-heavy since there's still only one of each 
case (and this quick'n'dirty copy-paste job didn't need any thought...)

If that's your preference too, though, I'll respin both driver patches 
that way.

Robin.

Re: [PATCH v7 6/6] iommu/arm-smmu: Support non-strict mode

[Robin Murphy]

On 2018-09-18 6:10 PM, Will Deacon wrote:
> On Fri, Sep 14, 2018 at 03:30:24PM +0100, Robin Murphy wrote:
>> All we need is to wire up .flush_iotlb_all properly and implement the
>> domain attribute, and iommu-dma and io-pgtable-arm will do the rest for
>> us. Rather than bother implementing it for v7s format for the highly
>> unlikely chance of that being relevant, we can simply hide the
>> non-strict flag from io-pgtable for that combination just so anyone who
>> does actually try it will simply get over-invalidation instead of
>> failure to initialise domains.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   drivers/iommu/arm-smmu.c | 40 +++++++++++++++++++++++++++++++++-------
>>   1 file changed, 33 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index fd1b80ef9490..aa5be334753b 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -246,6 +246,7 @@ struct arm_smmu_domain {
>>   	const struct iommu_gather_ops	*tlb_ops;
>>   	struct arm_smmu_cfg		cfg;
>>   	enum arm_smmu_domain_stage	stage;
>> +	bool				non_strict;
>>   	struct mutex			init_mutex; /* Protects smmu pointer */
>>   	spinlock_t			cb_lock; /* Serialises ATS1* ops and TLB syncs */
>>   	struct iommu_domain		domain;
>> @@ -863,6 +864,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>>   	if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK)
>>   		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>>   
>> +	if (smmu_domain->non_strict && cfg->fmt != ARM_SMMU_CTX_FMT_AARCH32_S)
>> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> 
> Does this mean we end up over-invalidating when using short-descriptor?
> Could we not bypass the flush queue in this case instead? Ideally, we'd
> just reject the domain attribute but I don't know if we know about the
> page-table format early enough for that. Alternatively, we could force
> long format if the attribute is set.
> 
> What do you think?

If someone manages to run an arm64 kernel on a theoretical SMMUv2 
implementation which only supports short-descriptor, *and* explicitly 
sets the command-line option, then yes, they'll get both the synchronous 
TLBIs and the periodic TLBIALLs. As implied by the commit message, my 
natural response is "don't do that".

However, it will almost certainly take more effort to argue about it or 
come up with other bodges than it will to just implement the quirk in 
the v7s code, so if you really think it's a valid concern just shout.

Robin.