Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

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Hi Leon,

On 1/14/21 9:26 PM, Leon Romanovsky wrote:
On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote:
Some vendor IOMMU drivers are able to declare that it is running in a VM
context. This is very valuable for the features that only want to be
supported on bare metal. Add a capability bit so that it could be used.

And how is it used? Who and how will set it?

Use the existing iommu_capable(). I should add more descriptions about
who and how to use it.



Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
  drivers/iommu/intel/iommu.c  | 20 ++++++++++++++++++++
  drivers/iommu/virtio-iommu.c |  9 +++++++++
  include/linux/iommu.h        |  1 +
  3 files changed, 30 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index cb205a04fe4c..8eb022d0e8aa 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
  	return ret;
  }

+static inline bool caching_mode_enabled(void)
+{

Kernel coding style is not in favour of inline functions in *.c files.

Yes, agreed.

Best regards,
baolu


+	struct dmar_drhd_unit *drhd;
+	struct intel_iommu *iommu;
+	bool ret = false;
+
+	rcu_read_lock();
+	for_each_active_iommu(iommu, drhd) {
+		if (cap_caching_mode(iommu->cap)) {
+			ret = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
  static bool intel_iommu_capable(enum iommu_cap cap)
  {
  	if (cap == IOMMU_CAP_CACHE_COHERENCY)
  		return domain_update_iommu_snooping(NULL) == 1;
  	if (cap == IOMMU_CAP_INTR_REMAP)
  		return irq_remapping_enabled == 1;
+	if (cap == IOMMU_CAP_VIOMMU)
+		return caching_mode_enabled();

  	return false;
  }
diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 2bfdd5734844..719793e103db 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
  	return iommu_fwspec_add_ids(dev, args->args, 1);
  }

+static bool viommu_capable(enum iommu_cap cap)
+{
+	if (cap == IOMMU_CAP_VIOMMU)
+		return true;
+
+	return false;
+}
+
  static struct iommu_ops viommu_ops = {
+	.capable		= viommu_capable,
  	.domain_alloc		= viommu_domain_alloc,
  	.domain_free		= viommu_domain_free,
  	.attach_dev		= viommu_attach_dev,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index b95a6f8db6ff..1d24be667a03 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -94,6 +94,7 @@ enum iommu_cap {
  					   transactions */
  	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
  	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
+	IOMMU_CAP_VIOMMU,		/* IOMMU can declar running in a VM */
  };

  /*
--
2.25.1




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