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Date:   Sat, 16 Jan 2021 09:20:16 +0800
From:   Lu Baolu <>
To:     Leon Romanovsky <>
Subject: Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU


On 2021/1/15 14:31, Leon Romanovsky wrote:
> On Fri, Jan 15, 2021 at 07:49:47AM +0800, Lu Baolu wrote:
>> 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.
> 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)
  		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;


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

Best regards,

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