diff mbox series

[14/17] iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE

Message ID 20210301084257.945454-15-hch@lst.de
State New
Headers show
Series [01/17] iommu: remove the unused domain_window_disable method | expand

Commit Message

Christoph Hellwig March 1, 2021, 8:42 a.m. UTC
Use explicit methods for setting and querying the information instead.

Also remove the now unused iommu_domain_get_attr functionality.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/iommu/amd/iommu.c                   | 23 ++-------
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 47 ++++++-----------
 drivers/iommu/arm/arm-smmu/arm-smmu.c       | 56 +++++----------------
 drivers/iommu/dma-iommu.c                   |  8 ++-
 drivers/iommu/intel/iommu.c                 | 27 ++--------
 drivers/iommu/iommu.c                       | 19 +++----
 include/linux/iommu.h                       | 17 ++-----
 7 files changed, 51 insertions(+), 146 deletions(-)

Comments

Christoph Hellwig March 10, 2021, 8:54 a.m. UTC | #1
On Thu, Mar 04, 2021 at 03:25:27PM +0000, Robin Murphy wrote:
> On 2021-03-01 08:42, Christoph Hellwig wrote:

>> Use explicit methods for setting and querying the information instead.

>

> Now that everyone's using iommu-dma, is there any point in bouncing this 

> through the drivers at all? Seems like it would make more sense for the x86 

> drivers to reflect their private options back to iommu_dma_strict (and 

> allow Intel's caching mode to override it as well), then have 

> iommu_dma_init_domain just test !iommu_dma_strict && 

> domain->ops->flush_iotlb_all.


Indeed.  I switch to that.
Christoph Hellwig March 10, 2021, 9:15 a.m. UTC | #2
On Thu, Mar 04, 2021 at 03:25:27PM +0000, Robin Murphy wrote:
> On 2021-03-01 08:42, Christoph Hellwig wrote:
>> Use explicit methods for setting and querying the information instead.
>
> Now that everyone's using iommu-dma, is there any point in bouncing this 
> through the drivers at all? Seems like it would make more sense for the x86 
> drivers to reflect their private options back to iommu_dma_strict (and 
> allow Intel's caching mode to override it as well), then have 
> iommu_dma_init_domain just test !iommu_dma_strict && 
> domain->ops->flush_iotlb_all.

Hmm.  I looked at this, and kill off ->dma_enable_flush_queue for
the ARM drivers and just looking at iommu_dma_strict seems like a
very clear win.

OTOH x86 is a little more complicated.  AMD and intel defaul to lazy
mode, so we'd have to change the global iommu_dma_strict if they are
initialized.  Also Intel has not only a "static" option to disable
lazy mode, but also a "dynamic" one where it iterates structure.  So
I think on the get side we're stuck with the method, but it still
simplifies the whole thing.
Christoph Hellwig March 10, 2021, 9:25 a.m. UTC | #3
On Wed, Mar 10, 2021 at 10:15:01AM +0100, Christoph Hellwig wrote:
> On Thu, Mar 04, 2021 at 03:25:27PM +0000, Robin Murphy wrote:

> > On 2021-03-01 08:42, Christoph Hellwig wrote:

> >> Use explicit methods for setting and querying the information instead.

> >

> > Now that everyone's using iommu-dma, is there any point in bouncing this 

> > through the drivers at all? Seems like it would make more sense for the x86 

> > drivers to reflect their private options back to iommu_dma_strict (and 

> > allow Intel's caching mode to override it as well), then have 

> > iommu_dma_init_domain just test !iommu_dma_strict && 

> > domain->ops->flush_iotlb_all.

> 

> Hmm.  I looked at this, and kill off ->dma_enable_flush_queue for

> the ARM drivers and just looking at iommu_dma_strict seems like a

> very clear win.

> 

> OTOH x86 is a little more complicated.  AMD and intel defaul to lazy

> mode, so we'd have to change the global iommu_dma_strict if they are

> initialized.  Also Intel has not only a "static" option to disable

> lazy mode, but also a "dynamic" one where it iterates structure.  So

> I think on the get side we're stuck with the method, but it still

> simplifies the whole thing.


Actually... Just mirroring the iommu_dma_strict value into
struct iommu_domain should solve all of that with very little
boilerplate code.
Robin Murphy March 10, 2021, 6:39 p.m. UTC | #4
On 2021-03-10 09:25, Christoph Hellwig wrote:
> On Wed, Mar 10, 2021 at 10:15:01AM +0100, Christoph Hellwig wrote:
>> On Thu, Mar 04, 2021 at 03:25:27PM +0000, Robin Murphy wrote:
>>> On 2021-03-01 08:42, Christoph Hellwig wrote:
>>>> Use explicit methods for setting and querying the information instead.
>>>
>>> Now that everyone's using iommu-dma, is there any point in bouncing this
>>> through the drivers at all? Seems like it would make more sense for the x86
>>> drivers to reflect their private options back to iommu_dma_strict (and
>>> allow Intel's caching mode to override it as well), then have
>>> iommu_dma_init_domain just test !iommu_dma_strict &&
>>> domain->ops->flush_iotlb_all.
>>
>> Hmm.  I looked at this, and kill off ->dma_enable_flush_queue for
>> the ARM drivers and just looking at iommu_dma_strict seems like a
>> very clear win.
>>
>> OTOH x86 is a little more complicated.  AMD and intel defaul to lazy
>> mode, so we'd have to change the global iommu_dma_strict if they are
>> initialized.  Also Intel has not only a "static" option to disable
>> lazy mode, but also a "dynamic" one where it iterates structure.  So
>> I think on the get side we're stuck with the method, but it still
>> simplifies the whole thing.
> 
> Actually... Just mirroring the iommu_dma_strict value into
> struct iommu_domain should solve all of that with very little
> boilerplate code.

Yes, my initial thought was to directly replace the attribute with a
common flag at iommu_domain level, but since in all cases the behaviour
is effectively global rather than actually per-domain, it seemed
reasonable to take it a step further. This passes compile-testing for
arm64 and x86, what do you think?

Robin.

----->8-----
Subject: [PATCH] iommu: Consolidate strict invalidation handling

Now that everyone is using iommu-dma, the global invalidation policy
really doesn't need to be woven through several parts of the core API
and individual drivers, we can just look it up directly at the one point
that we now make the flush queue decision. If the x86 drivers reflect
their internal options and overrides back to iommu_dma_strict, that can
become the canonical source.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
  drivers/iommu/amd/iommu.c   |  2 ++
  drivers/iommu/dma-iommu.c   |  8 +-------
  drivers/iommu/intel/iommu.c | 12 ++++++++++++
  drivers/iommu/iommu.c       | 35 +++++++++++++++++++++++++++--------
  include/linux/iommu.h       |  2 ++
  5 files changed, 44 insertions(+), 15 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index a69a8b573e40..1db29e59d468 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1856,6 +1856,8 @@ int __init amd_iommu_init_dma_ops(void)
  	else
  		pr_info("Lazy IO/TLB flushing enabled\n");
  
+	iommu_set_dma_strict(amd_iommu_unmap_flush);
+
  	return 0;
  
  }
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index af765c813cc8..789a950cc125 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -304,10 +304,6 @@ static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
  
  	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
  	domain = cookie->fq_domain;
-	/*
-	 * The IOMMU driver supporting DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE
-	 * implies that ops->flush_iotlb_all must be non-NULL.
-	 */
  	domain->ops->flush_iotlb_all(domain);
  }
  
@@ -334,7 +330,6 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
  	struct iommu_dma_cookie *cookie = domain->iova_cookie;
  	unsigned long order, base_pfn;
  	struct iova_domain *iovad;
-	int attr;
  
  	if (!cookie || cookie->type != IOMMU_DMA_IOVA_COOKIE)
  		return -EINVAL;
@@ -371,8 +366,7 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
  	init_iova_domain(iovad, 1UL << order, base_pfn);
  
  	if (!cookie->fq_domain && (!dev || !dev_is_untrusted(dev)) &&
-	    !iommu_domain_get_attr(domain, DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, &attr) &&
-	    attr) {
+	    domain->ops->flush_iotlb_all && !iommu_get_dma_strict()) {
  		if (init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all,
  					  iommu_dma_entry_dtor))
  			pr_warn("iova flush queue initialization failed\n");
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index b5c746f0f63b..f5b452cd1266 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4377,6 +4377,17 @@ int __init intel_iommu_init(void)
  
  	down_read(&dmar_global_lock);
  	for_each_active_iommu(iommu, drhd) {
+		if (!intel_iommu_strict && cap_caching_mode(iommu->cap)) {
+			/*
+			 * The flush queue implementation does not perform page-selective
+			 * invalidations that are required for efficient TLB flushes in
+			 * virtual environments. The benefit of batching is likely to be
+			 * much lower than the overhead of synchronizing the virtual and
+			 * physical IOMMU page-tables.
+			 */
+			pr_warn("IOMMU batching is disabled due to virtualization");
+			intel_iommu_strict = 1;
+		}
  		iommu_device_sysfs_add(&iommu->iommu, NULL,
  				       intel_iommu_groups,
  				       "%s", iommu->name);
@@ -4384,6 +4395,7 @@ int __init intel_iommu_init(void)
  	}
  	up_read(&dmar_global_lock);
  
+	iommu_set_dma_strict(intel_iommu_strict);
  	bus_set_iommu(&pci_bus_type, &intel_iommu_ops);
  	if (si_domain && !hw_pass_through)
  		register_memory_notifier(&intel_iommu_memory_nb);
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 2f3399203813..80afcf50cd3c 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -69,6 +69,7 @@ static const char * const iommu_group_resv_type_string[] = {
  };
  
  #define IOMMU_CMD_LINE_DMA_API		BIT(0)
+#define IOMMU_CMD_LINE_STRICT		BIT(1)
  
  static void iommu_set_cmd_line_dma_api(void)
  {
@@ -80,6 +81,16 @@ static bool iommu_cmd_line_dma_api(void)
  	return !!(iommu_cmd_line & IOMMU_CMD_LINE_DMA_API);
  }
  
+static void iommu_set_cmd_line_strict(void)
+{
+	iommu_cmd_line |= IOMMU_CMD_LINE_STRICT;
+}
+
+static bool iommu_cmd_line_strict(void)
+{
+	return !!(iommu_cmd_line & IOMMU_CMD_LINE_STRICT);
+}
+
  static int iommu_alloc_default_domain(struct iommu_group *group,
  				      struct device *dev);
  static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
@@ -337,10 +348,25 @@ early_param("iommu.passthrough", iommu_set_def_domain_type);
  
  static int __init iommu_dma_setup(char *str)
  {
-	return kstrtobool(str, &iommu_dma_strict);
+	int ret = kstrtobool(str, &iommu_dma_strict);
+
+	if (!ret)
+		iommu_set_cmd_line_strict();
+	return ret;
  }
  early_param("iommu.strict", iommu_dma_setup);
  
+void iommu_set_dma_strict(bool val)
+{
+	if (val || !iommu_cmd_line_strict())
+		iommu_dma_strict = val;
+}
+
+bool iommu_get_dma_strict(void)
+{
+	return iommu_dma_strict;
+}
+
  static ssize_t iommu_group_attr_show(struct kobject *kobj,
  				     struct attribute *__attr, char *buf)
  {
@@ -1520,13 +1546,6 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus,
  	if (!group->domain)
  		group->domain = dom;
  
-	if (!iommu_dma_strict) {
-		int attr = 1;
-		iommu_domain_set_attr(dom,
-				      DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
-				      &attr);
-	}
-
  	return 0;
  }
  
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index eb5e3f14c5ad..11bbfa273d98 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -495,6 +495,8 @@ extern int iommu_domain_get_attr(struct iommu_domain *domain, enum iommu_attr,
  				 void *data);
  extern int iommu_domain_set_attr(struct iommu_domain *domain, enum iommu_attr,
  				 void *data);
+extern void iommu_set_dma_strict(bool val);
+extern bool iommu_get_dma_strict(void);
  
  /* Window handling function prototypes */
  extern int iommu_domain_window_enable(struct iommu_domain *domain, u32 wnd_nr,
Christoph Hellwig March 11, 2021, 8:26 a.m. UTC | #5
On Wed, Mar 10, 2021 at 06:39:57PM +0000, Robin Murphy wrote:
>> Actually... Just mirroring the iommu_dma_strict value into
>> struct iommu_domain should solve all of that with very little
>> boilerplate code.
>
> Yes, my initial thought was to directly replace the attribute with a
> common flag at iommu_domain level, but since in all cases the behaviour
> is effectively global rather than actually per-domain, it seemed
> reasonable to take it a step further. This passes compile-testing for
> arm64 and x86, what do you think?

It seems to miss a few bits, and also generally seems to be not actually
apply to recent mainline or something like it due to different empty
lines in a few places.

Let me know what you think of the version here:

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/iommu-cleanup

I'll happily switch the patch to you as the author if you're fine with
that as well.
Robin Murphy March 12, 2021, 4:18 p.m. UTC | #6
On 2021-03-11 08:26, Christoph Hellwig wrote:
> On Wed, Mar 10, 2021 at 06:39:57PM +0000, Robin Murphy wrote:
>>> Actually... Just mirroring the iommu_dma_strict value into
>>> struct iommu_domain should solve all of that with very little
>>> boilerplate code.
>>
>> Yes, my initial thought was to directly replace the attribute with a
>> common flag at iommu_domain level, but since in all cases the behaviour
>> is effectively global rather than actually per-domain, it seemed
>> reasonable to take it a step further. This passes compile-testing for
>> arm64 and x86, what do you think?
> 
> It seems to miss a few bits, and also generally seems to be not actually
> apply to recent mainline or something like it due to different empty
> lines in a few places.

Yeah, that was sketched out on top of some other development patches, 
and in being so focused on not breaking any of the x86 behaviours I did 
indeed overlook fully converting the SMMU drivers... oops!

(my thought was to do the conversion for its own sake, then clean up the 
redundant attribute separately, but I guess it's fine either way)

> Let me know what you think of the version here:
> 
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/iommu-cleanup
> 
> I'll happily switch the patch to you as the author if you're fine with
> that as well.

I still have reservations about removing the attribute API entirely and 
pretending that io_pgtable_cfg is anything other than a SoC-specific 
private interface, but the reworked patch on its own looks reasonable to 
me, thanks! (I wasn't too convinced about the iommu_cmd_line wrappers 
either...) Just iommu_get_dma_strict() needs an export since the SMMU 
drivers can be modular - I consciously didn't add that myself since I 
was mistakenly thinking only iommu-dma would call it.

Robin.
Christoph Hellwig March 15, 2021, 8:33 a.m. UTC | #7
On Fri, Mar 12, 2021 at 04:18:24PM +0000, Robin Murphy wrote:
>> Let me know what you think of the version here:
>>
>> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/iommu-cleanup
>>
>> I'll happily switch the patch to you as the author if you're fine with
>> that as well.
>
> I still have reservations about removing the attribute API entirely and 
> pretending that io_pgtable_cfg is anything other than a SoC-specific 
> private interface,

I think a private inteface would make more sense.  For now I've just
condensed it down to a generic set of quirk bits and dropped the
attrs structure, which seems like an ok middle ground for now.  That
being said I wonder why that quirk isn't simply set in the device
tree?

> but the reworked patch on its own looks reasonable to 
> me, thanks! (I wasn't too convinced about the iommu_cmd_line wrappers 
> either...) Just iommu_get_dma_strict() needs an export since the SMMU 
> drivers can be modular - I consciously didn't add that myself since I was 
> mistakenly thinking only iommu-dma would call it.

Fixed.  Can I get your signoff for the patch?  Then I'll switch it to
over to being attributed to you.
diff mbox series

Patch

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index a69a8b573e40d0..37a8e51db17656 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1771,24 +1771,11 @@  static struct iommu_group *amd_iommu_device_group(struct device *dev)
 	return acpihid_device_group(dev);
 }
 
-static int amd_iommu_domain_get_attr(struct iommu_domain *domain,
-		enum iommu_attr attr, void *data)
+static bool amd_iommu_dma_use_flush_queue(struct iommu_domain *domain)
 {
-	switch (domain->type) {
-	case IOMMU_DOMAIN_UNMANAGED:
-		return -ENODEV;
-	case IOMMU_DOMAIN_DMA:
-		switch (attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
-			*(int *)data = !amd_iommu_unmap_flush;
-			return 0;
-		default:
-			return -ENODEV;
-		}
-		break;
-	default:
-		return -EINVAL;
-	}
+	if (domain->type != IOMMU_DOMAIN_DMA)
+		return false;
+	return !amd_iommu_unmap_flush;
 }
 
 /*****************************************************************************
@@ -2257,7 +2244,7 @@  const struct iommu_ops amd_iommu_ops = {
 	.release_device = amd_iommu_release_device,
 	.probe_finalize = amd_iommu_probe_finalize,
 	.device_group = amd_iommu_device_group,
-	.domain_get_attr = amd_iommu_domain_get_attr,
+	.dma_use_flush_queue = amd_iommu_dma_use_flush_queue,
 	.get_resv_regions = amd_iommu_get_resv_regions,
 	.put_resv_regions = generic_iommu_put_resv_regions,
 	.is_attach_deferred = amd_iommu_is_attach_deferred,
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 8594b4a8304375..bf96172e8c1f71 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2449,33 +2449,21 @@  static struct iommu_group *arm_smmu_device_group(struct device *dev)
 	return group;
 }
 
-static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
-				    enum iommu_attr attr, void *data)
+static bool arm_smmu_dma_use_flush_queue(struct iommu_domain *domain)
 {
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	switch (domain->type) {
-	case IOMMU_DOMAIN_UNMANAGED:
-		switch (attr) {
-		case DOMAIN_ATTR_NESTING:
-			*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
-			return 0;
-		default:
-			return -ENODEV;
-		}
-		break;
-	case IOMMU_DOMAIN_DMA:
-		switch (attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
-			*(int *)data = smmu_domain->non_strict;
-			return 0;
-		default:
-			return -ENODEV;
-		}
-		break;
-	default:
-		return -EINVAL;
-	}
+	if (domain->type != IOMMU_DOMAIN_DMA)
+		return false;
+	return smmu_domain->non_strict;
+}
+
+
+static void arm_smmu_dma_enable_flush_queue(struct iommu_domain *domain)
+{
+	if (domain->type != IOMMU_DOMAIN_DMA)
+		return;
+	to_smmu_domain(domain)->non_strict = true;
 }
 
 static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
@@ -2505,13 +2493,7 @@  static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 		}
 		break;
 	case IOMMU_DOMAIN_DMA:
-		switch(attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
-			smmu_domain->non_strict = *(int *)data;
-			break;
-		default:
-			ret = -ENODEV;
-		}
+		ret = -ENODEV;
 		break;
 	default:
 		ret = -EINVAL;
@@ -2619,7 +2601,8 @@  static struct iommu_ops arm_smmu_ops = {
 	.probe_device		= arm_smmu_probe_device,
 	.release_device		= arm_smmu_release_device,
 	.device_group		= arm_smmu_device_group,
-	.domain_get_attr	= arm_smmu_domain_get_attr,
+	.dma_use_flush_queue	= arm_smmu_dma_use_flush_queue,
+	.dma_enable_flush_queue	= arm_smmu_dma_enable_flush_queue,
 	.domain_set_attr	= arm_smmu_domain_set_attr,
 	.of_xlate		= arm_smmu_of_xlate,
 	.get_resv_regions	= arm_smmu_get_resv_regions,
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index d8c6bfde6a6158..e7893e96f5177a 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -1481,42 +1481,20 @@  static struct iommu_group *arm_smmu_device_group(struct device *dev)
 	return group;
 }
 
-static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
-				    enum iommu_attr attr, void *data)
+static bool arm_smmu_dma_use_flush_queue(struct iommu_domain *domain)
 {
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 
-	switch(domain->type) {
-	case IOMMU_DOMAIN_UNMANAGED:
-		switch (attr) {
-		case DOMAIN_ATTR_NESTING:
-			*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
-			return 0;
-		case DOMAIN_ATTR_IO_PGTABLE_CFG: {
-			struct io_pgtable_domain_attr *pgtbl_cfg = data;
-			*pgtbl_cfg = smmu_domain->pgtbl_cfg;
+	if (domain->type != IOMMU_DOMAIN_DMA)
+		return false;
+	return smmu_domain->pgtbl_cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT;
+}
 
-			return 0;
-		}
-		default:
-			return -ENODEV;
-		}
-		break;
-	case IOMMU_DOMAIN_DMA:
-		switch (attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE: {
-			bool non_strict = smmu_domain->pgtbl_cfg.quirks &
-					  IO_PGTABLE_QUIRK_NON_STRICT;
-			*(int *)data = non_strict;
-			return 0;
-		}
-		default:
-			return -ENODEV;
-		}
-		break;
-	default:
-		return -EINVAL;
-	}
+static void arm_smmu_dma_enable_flush_queue(struct iommu_domain *domain)
+{
+	if (domain->type != IOMMU_DOMAIN_DMA)
+		return;
+	to_smmu_domain(domain)->pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
 }
 
 static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
@@ -1557,16 +1535,7 @@  static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 		}
 		break;
 	case IOMMU_DOMAIN_DMA:
-		switch (attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
-			if (*(int *)data)
-				smmu_domain->pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
-			else
-				smmu_domain->pgtbl_cfg.quirks &= ~IO_PGTABLE_QUIRK_NON_STRICT;
-			break;
-		default:
-			ret = -ENODEV;
-		}
+		ret = -ENODEV;
 		break;
 	default:
 		ret = -EINVAL;
@@ -1631,7 +1600,8 @@  static struct iommu_ops arm_smmu_ops = {
 	.probe_device		= arm_smmu_probe_device,
 	.release_device		= arm_smmu_release_device,
 	.device_group		= arm_smmu_device_group,
-	.domain_get_attr	= arm_smmu_domain_get_attr,
+	.dma_use_flush_queue	= arm_smmu_dma_use_flush_queue,
+	.dma_enable_flush_queue	= arm_smmu_dma_enable_flush_queue,
 	.domain_set_attr	= arm_smmu_domain_set_attr,
 	.of_xlate		= arm_smmu_of_xlate,
 	.get_resv_regions	= arm_smmu_get_resv_regions,
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 9ab6ee22c11088..d3fe5aad9d6ecf 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -305,8 +305,8 @@  static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
 	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
 	domain = cookie->fq_domain;
 	/*
-	 * The IOMMU driver supporting DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE
-	 * implies that ops->flush_iotlb_all must be non-NULL.
+	 * The IOMMU driver supporting a DMA flush queue implies that
+	 * ops->flush_iotlb_all must be non-NULL.
 	 */
 	domain->ops->flush_iotlb_all(domain);
 }
@@ -329,7 +329,6 @@  static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
 	unsigned long order, base_pfn;
 	struct iova_domain *iovad;
-	int attr;
 
 	if (!cookie || cookie->type != IOMMU_DMA_IOVA_COOKIE)
 		return -EINVAL;
@@ -365,8 +364,7 @@  static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 
 	init_iova_domain(iovad, 1UL << order, base_pfn);
 
-	if (!cookie->fq_domain && !iommu_domain_get_attr(domain,
-			DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, &attr) && attr) {
+	if (!cookie->fq_domain && iommu_dma_use_flush_queue(domain)) {
 		if (init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all,
 					  iommu_dma_entry_dtor))
 			pr_warn("iova flush queue initialization failed\n");
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index ee0932307d646b..eaa80c33f4bc91 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -5453,13 +5453,13 @@  intel_iommu_domain_set_attr(struct iommu_domain *domain,
 	return ret;
 }
 
-static bool domain_use_flush_queue(void)
+static bool intel_iommu_dma_use_flush_queue(struct iommu_domain *domain)
 {
 	struct dmar_drhd_unit *drhd;
 	struct intel_iommu *iommu;
 	bool r = true;
 
-	if (intel_iommu_strict)
+	if (domain->type != IOMMU_DOMAIN_DMA || intel_iommu_strict)
 		return false;
 
 	/*
@@ -5483,27 +5483,6 @@  static bool domain_use_flush_queue(void)
 	return r;
 }
 
-static int
-intel_iommu_domain_get_attr(struct iommu_domain *domain,
-			    enum iommu_attr attr, void *data)
-{
-	switch (domain->type) {
-	case IOMMU_DOMAIN_UNMANAGED:
-		return -ENODEV;
-	case IOMMU_DOMAIN_DMA:
-		switch (attr) {
-		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
-			*(int *)data = domain_use_flush_queue();
-			return 0;
-		default:
-			return -ENODEV;
-		}
-		break;
-	default:
-		return -EINVAL;
-	}
-}
-
 /*
  * Check that the device does not live on an external facing PCI port that is
  * marked as untrusted. Such devices should not be able to apply quirks and
@@ -5576,7 +5555,7 @@  const struct iommu_ops intel_iommu_ops = {
 	.capable		= intel_iommu_capable,
 	.domain_alloc		= intel_iommu_domain_alloc,
 	.domain_free		= intel_iommu_domain_free,
-	.domain_get_attr        = intel_iommu_domain_get_attr,
+	.dma_use_flush_queue	= intel_iommu_dma_use_flush_queue,
 	.domain_set_attr	= intel_iommu_domain_set_attr,
 	.attach_dev		= intel_iommu_attach_device,
 	.detach_dev		= intel_iommu_detach_device,
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 23daaea7883b75..0f12c4d58cdc42 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1512,12 +1512,8 @@  static int iommu_group_alloc_default_domain(struct bus_type *bus,
 	if (!group->domain)
 		group->domain = dom;
 
-	if (!iommu_dma_strict) {
-		int attr = 1;
-		iommu_domain_set_attr(dom,
-				      DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
-				      &attr);
-	}
+	if (!iommu_dma_strict && dom->ops->dma_enable_flush_queue)
+		dom->ops->dma_enable_flush_queue(dom);
 
 	return 0;
 }
@@ -2664,14 +2660,13 @@  static int __init iommu_init(void)
 }
 core_initcall(iommu_init);
 
-int iommu_domain_get_attr(struct iommu_domain *domain,
-			  enum iommu_attr attr, void *data)
+bool iommu_dma_use_flush_queue(struct iommu_domain *domain)
 {
-	if (!domain->ops->domain_get_attr)
-		return -EINVAL;
-	return domain->ops->domain_get_attr(domain, attr, data);
+	if (!domain->ops->dma_use_flush_queue)
+		return false;
+	return domain->ops->dma_use_flush_queue(domain);
 }
-EXPORT_SYMBOL_GPL(iommu_domain_get_attr);
+EXPORT_SYMBOL_GPL(iommu_dma_use_flush_queue);
 
 int iommu_domain_set_attr(struct iommu_domain *domain,
 			  enum iommu_attr attr, void *data)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index c15a8658daad64..f30de33c6ff56e 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -108,7 +108,6 @@  enum iommu_cap {
 
 enum iommu_attr {
 	DOMAIN_ATTR_NESTING,	/* two stages of translation */
-	DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
 	DOMAIN_ATTR_IO_PGTABLE_CFG,
 	DOMAIN_ATTR_MAX,
 };
@@ -194,7 +193,8 @@  struct iommu_iotlb_gather {
  * @probe_finalize: Do final setup work after the device is added to an IOMMU
  *                  group and attached to the groups domain
  * @device_group: find iommu group for a particular device
- * @domain_get_attr: Query domain attributes
+ * @dma_use_flush_queue: Returns %true if a DMA flush queue is used
+ * @dma_enable_flush_queue: Try to enable the DMA flush queue
  * @domain_set_attr: Change domain attributes
  * @get_resv_regions: Request list of reserved regions for a device
  * @put_resv_regions: Free list of reserved regions for a device
@@ -244,8 +244,8 @@  struct iommu_ops {
 	void (*release_device)(struct device *dev);
 	void (*probe_finalize)(struct device *dev);
 	struct iommu_group *(*device_group)(struct device *dev);
-	int (*domain_get_attr)(struct iommu_domain *domain,
-			       enum iommu_attr attr, void *data);
+	bool (*dma_use_flush_queue)(struct iommu_domain *domain);
+	void (*dma_enable_flush_queue)(struct iommu_domain *domain);
 	int (*domain_set_attr)(struct iommu_domain *domain,
 			       enum iommu_attr attr, void *data);
 
@@ -491,8 +491,7 @@  extern int iommu_page_response(struct device *dev,
 extern int iommu_group_id(struct iommu_group *group);
 extern struct iommu_domain *iommu_group_default_domain(struct iommu_group *);
 
-extern int iommu_domain_get_attr(struct iommu_domain *domain, enum iommu_attr,
-				 void *data);
+bool iommu_dma_use_flush_queue(struct iommu_domain *domain);
 extern int iommu_domain_set_attr(struct iommu_domain *domain, enum iommu_attr,
 				 void *data);
 
@@ -861,12 +860,6 @@  static inline int iommu_group_id(struct iommu_group *group)
 	return -ENODEV;
 }
 
-static inline int iommu_domain_get_attr(struct iommu_domain *domain,
-					enum iommu_attr attr, void *data)
-{
-	return -EINVAL;
-}
-
 static inline int iommu_domain_set_attr(struct iommu_domain *domain,
 					enum iommu_attr attr, void *data)
 {