Hi Leon,

On 2021/1/16 16:39, Leon Romanovsky wrote:

On Sat, Jan 16, 2021 at 09:20:16AM +0800, Lu Baolu wrote:

quoted

Hi,

On 2021/1/15 14:31, Leon Romanovsky wrote:

quoted

On Fri, Jan 15, 2021 at 07:49:47AM +0800, Lu Baolu wrote:

quoted

Hi Leon,

On 1/14/21 9:26 PM, Leon Romanovsky wrote:

quoted

On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote:

quoted

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.

I want to see the code that sets this capability.

Currently we have Intel VT-d and the virt-iommu setting this capability.

  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;
  }

And,

+static bool viommu_capable(enum iommu_cap cap)
+{
+	if (cap == IOMMU_CAP_VIOMMU)
+		return true;
+
+	return false;
+}

These two functions are reading this cap and not setting.
Where can I see code that does "cap = IOMMU_CAP_VIOMMU" and not "=="?

The iommu_capable() is a generic IOMMU interface to query IOMMU
capabilities. It takes @bus and @cap as input, and calls the callback
of vendor iommu. If the vendor iommu driver supports the specific
capability, it returns true. Otherwise, it returns false.

bool iommu_capable(struct bus_type *bus, enum iommu_cap cap)
{
         if (!bus->iommu_ops || !bus->iommu_ops->capable)
                 return false;

         return bus->iommu_ops->capable(cap);
}
EXPORT_SYMBOL_GPL(iommu_capable);

In the vendor iommu's callback, it checks the capability and returns a
value according to its capability, just as showed above.

Best regards,
baolu